We all know that we have been told that heaver pellets will damage your rifle, But why when you do the math on a rifle like the 2 barrel Beeman ( 177 & 22 cal) Say we use a set of numbers like 900 fps with a 7.9 gr. (177 cal )pellet you get 14.21 ft. lbs of energy and the same ft. lbs energy of 14.21 using 14.3 gr. ( 22cal) pellets you get a fps of 668. now why if you were to use a 14.3 gr pellet in a 177 cal ( if you could get them )why would it hurt your rifle since the energy is the same and if you change the barrel you don't change the transfer port or do any thing else . I don't see how it will hurt your rifle You are only changing the pellet weight the fps changes when you do this automatically .howie
Its air ratio in the larger barrel that is less restrictive and does not cause the piston to bounce back on the spring causing early wear.
That being said, I am in the camp that if its heavy pellets you like and they are accurate SHOOT them! Springs are replaceable. I shot 11.5 grain Silver Arrows for a year out of a .177 Diana 34 and its fine as any gun.
Interesting. I've been told it's the light pellets that will damage a magnum springer. I believe the theory is that they do not permit sufficient resistance to keep the piston from slamming home and damaging the seal.
We all know that super light pellets damage an air gun (as evidenced by the lightest pellet of all, none!). At the other end of the spectrum is the super heavy pellet (e.g. weld the barrel shut!).
Somewhere in between is the right balance. The good news, as Chris mentioned is that the heavier pellets only cause the spring to tire prematurely.
I'm of the notion that too light pellets do more harm than too heavy pellets. Heavy pellets may or may not weaken a spring over time, but too light pellets or too loose pellets might let the piston slam into the chamber and do far more than just weaken a spring.
The difference in a rifle where you only change the caliber is what in Internal Ballistics is called Expansion Ratio. It works in firearms and also in pellet guns.
The most intuitive way of explaining expansion ratio is by making you think of the following:
The piston is in front of the same spring, right?
It has the same weight, same area, same impulse.
Therefore, it is expected that the powerplant will develop the same pressure curve/spike, right?
OK, now, think in terms of pressure: Force divided by an area.
If the pressure is applied in a small area (0.177" cal. pellet) it will produce some force; BUT if it is appplied over a LARGER area, like a .22" pellet, it will produce MORE force.
So, we say that the expansion ratio of bigger calibers is better for the same pressure curve. Ergo, there is MORE energy TRANSFER from the powerplant to the projectile.
If a powerplant cannot transfer all its energy to the projectile, it has to go somewhere. In firearms it goes up in flash and smoke, literally. In Spring guns it goes BACK into the mechanism, either as piston slam, or as spring overcycling.
THIS is what damages the gun. Either too heavy or too light, is not good.
Airgunning, as most things in life is the "art of a happy medium".
Every now and then we DO find exceptional barrels that shoot well the heavy for caliber pellets there are out there in the market. In that instance, by all means, if they shoot well, use them.
But do bear in mind that the gun itself tells you where she is happy.
She will transfer the highest amount of energy to the pellet where she reaches her OWN happy medium.
That is why we all need some access to a Chrono, to see where our guns are happy. I'm not saying that we should all buy one, I am just saying that the best way to determine which pellet weight is most useful to YOUR gun is by using one.
the pellet that develops the most kinetic energy in my air rifle (i.e. the one that manages to absorb most of the spring's dynamic energy) is a pretty heavy 10.30 grain one...
And even the heavier ones produce about 17ftLbs which is almost the same efficiency you get from the usuall "light" rifle pellets....
Where did the rest of the energy go in every case???
I can live with a little spring chatter, but can't stand knowing that my piston slams every time i pull the trigger. After all the springs are considered consumables in springers - but not the pistons and compression cylinders - right?
Perhaps the spring in your gun is one which can handle both a .177 and a .22 pellet? (i.e. - does Diana put a different spring in a .22 model 34 VS the .177? Probably not.) I think what hurts the spring is when you go quite a bit up in weight per caliber. You introduce a higher inertia with the heavier pellet. This seems to be what causes more of the energy to be momentarily retained within the spring, resulting in premature wear/breakage. Could be I'm just blowing smoke, but it seems logical.
"Perhaps the spring in your gun is one which can handle both a .177 and a .22 pellet? (i.e. - does Diana put a different spring in a .22 model 34 VS the .177? Probably not.)"
the M34 in .177 and .22 cal. is the SAME in it's internals, being the sweep volume and the spring, piston, transfer port and seal
the breech is what changes the cal. with the barrel, everything behind the barrel is the SAME
SOOOOO!!!
the 34 in .177 uses the same internals and spring as the 34 in .22 cal.
and the pellets are from 5 to 21 gr. in either .177 cal and .22 cal
same platform, different grain pellets
if the .22 can handle the .21 gr. pellets WHY can't the .177 not do the same with the 10 gr. ones with the same spring, it is the same air rifle with different pellet weights
you don't have to be Sherlock Holmes on this one just Joe six pack
warren
and remember "it's 30% the gun and 70% the shooter"
Dimitris, this is not a MODEL question it is an INDIVIDUAL rifle question.
JSB's are good and it just may happen that YOUR D-54 gives its best performance with them, but it is not a given. It is not a surety. You need to try and find out for yourself if this is true or not. There are MANY variables in an airgun. Even 2 or 3 ft-lbs difference from a max of 20 still represents 15%. Imagine getting only 13 1/2 ounces per pounf of sugar, or getting 170 HP in a "muscle" car. 15% is a large difference.
Not to disparage StraightShooters, but the time I weighed the JSB Heavies, they were more like 10.12 than 10.3
And there are other things in those tables that make them ILLUSTRATIVE, not authoritative. They are really good tables, but they will not reflect 100% of all the guns.
In the case of light pellets, most of the energy is dissipated in vibrations and piston slam. In the case of heavy pellets, what you call spring chatter is what destroys the spring. Pistons can be regarded as replaceable, and in the case of the D-54 design, even the cylinder is easily replaceable. It is one of those too often overlooked things that make that design so dear to me. You can swap the WHOLE internals relatively easy. Try doing that with ANY breakbarrel! LOL!
On the other hand, it is difficult to swap calibers. Six of one and half a dozen of the other, both designs have their merits.
Red is quite correct in his appreciation of the inertial aspects. He only misses one aspect, and that is that bigger calibers can USE the pressure curve in a much shorter time. Therefore, a small caliber gun can have the same expansion ratio as a larger caliber one, but it needs a longer barrel.
I was looking at one of their tables and noticed that a fairly heavier pellet was listed as doing considerably more fps than the much light ones. It was either a fluke or an error, as the other heavy pellets were about where one would expect. I don't know if SS takes one gun for one session, one gun for a number of sessions or averages several guns (which would be more representative). As Hector says, the tables are nice for general reference, but your gun will behave in a unique way.
You leave out one important variable in your force per unit area analysis:
The TOTAL potential energy in the system (the compressed spring) is the same regardless of caliber.
As the spring releases this energy, it builds pressure in front of the pision, which acts on the area of the pellet (or bore diameter)and truely, for a larger diameter a greater force is applied.
However - for every force, there is an equal and opposite force. And a .22 caliber pellet weighs more than a .177. By nature of it being heavier, it provides more resistance to the pressure (opposing force) developed by the piston.
In your example, for a given spring/piston arrangement that develops a consistent pressure when released, regardless of caliber, a .22 cal pellet, given its larger diameter, would exit the barrel FASTER than a .177 due to the large force applied to it. Except for the fact that a .22 weighs more and takes more force to get moving. Ironically, all .177/.22 guns deliver lower velocity in .22 than .177.
Now, having read that "heavy pellets damage spring guns" so many times, I'm going to have to do some math (ugh!). The reasons being: 1)I respect Hector's experience (and others) that heavy pellets decrease spring life and are in fact "harder" on spring guns; 2) Given a fixed amount of potential energy for a cocked spring, there should be a mathmatical relationship between velocity, pellet weight, and pellet diameter. The fact that (generally) a given airgun model delivers (relatively) the same energy (as measured in ft-lbs based on pellet velocity) regardless of caliber, tends to follow the laws of physics.
What is lacking in my analysis is the energy lost engery due to friction, etc and any differences of lost energy between calibers. There's also some dymanics issues bound to be in this equation(which is not my strong point,) perhaps that are related to the rate at which pressure developes behind a .177 and .22 cal pellet....
Anyway, its an interesting topic that I'm going to spend some time with.
Good shooting to all and no disrespect to Hector who is a treasure chest of knowledge here at the Dianawerk Collective!
Insignificant when compared to the power of the force
July 2 2009, 5:24 AM
Run some math based on the decreased surface area of .177 vs .22 using Pi * R squared. That is your major difference of why heavier pellets have a bigger adverse affect in a .177. I liken it to the Battle of Thermopylae where the pass helped a small group delay a substantially larger group (that and all those military things like the power of a patriotic army of freemen defending native soil, the advantages of training, equipment, and good use of terrain as force multipliers, courage against overwhelming odds, etc.)
Again SHOT WHAT YOU WANT AND WHATS ACCURATE> SPRINGS ARE RENEWABLE> I shoot 21 Grain Kodiak's from my 350 all day. Stock Guns may not like them but once tuned you can shoot ANY pellet you want. I have gotten much better FT lbs sometimes with heavy pellets and better FPS as they create more load and back pressure and hold out till the last most powerful blast hits it ! Math or not If they are accurate SOOT THEM !
get a straw from Mcdonalds or Burger King and get another one from 7 Eleven, different diameters YES
now form a spit ball out of paper and with your lungs aspirate and exhale FAST pushing those spit ball's out to maximun output
there is no way to contradict Chis when he say's "I have gotten much better FT lbs sometimes with heavy pellets and better FPS as they create more load and back pressure and hold out till the last most powerful blast hits it". the 1.8 milli second before the pellet travels from the breech to the exit of the barrel is also KEY
the heavier the pellet the more back pressure in either caliber before the piston travels the full lengh of the strock
remember the formula: pellet weigh x velocity x velocity / by 45020 = FP meaning the heavier the pellet the less velocity and the more FP
velocity VS weight in the FP are completely different, the significant equation is the output capacity of the air gun, can an air gun shoot 14, 16, 18, 21 grain pellets compared to a magnum that can do it, like what can a M34 compared to the M350 shoot
decisions, decisions
warren
like some one said, to shoot or NOT to shoot
and remember "it's 30% the gun and 70% the shooter"
but soon will. We are talking about conservation of energy here. The cocked spring with the piston in front of it represents a FIXED amount of energy. The laws of physics dictate that that you cannot create any more energy in the system than this.
I read on a CO2 forum an interesting contradiction, that CO2 pellets deliver higher velocity than lighter pellets. This again appears to defy the laws of physics if on assume that the CO2 delivers the same pressure behind the pellet regardless of pellet weight. However, there where chrony listings to support that this was true. With numberous pellet brands and guns. So what gives -
I too had thought that the possible solution was that a heavier pellet resists motion longer, there for developes more pressure behind it, and then gets a harder push (ignoring diameter issues). This is my prevailing theory to support the reported CO2 numbers, but one cannot consider this with out considering the energy losses. I suspect there could be some differences between calibers and pellet weights.
And back to springers, if a heavier (or logically larger diameter) pellet provides more resistance to the spring, then this is simply more resistance against the release of the spring. Lowering a spring slower does not harm it. Just letting it go might not be good. Futher, letting it go against any pellet is better than no pellet, otherwise the spring/piston could slam into the front of the chamber.
I see some math in my future, unless someone sorts this out for me soon...There's alot of variables in this equation to sort out. The laws of physics always win in the end, so there's something missing in the explanations offered so far.....
I have heard of spring failing because of being compressed/extented beyond their elastic (yield) limit, left compressed for long periods of time, being suddenly released and let expand uncontrollably, but never a spring breaking due to gradual release.
The way I see it (and I am anxiously expecting Model48's math to prove it) is that the heavier/larger caliper/softer lead alloy /tighter fit/rougher rifling/tighter barrel choke (all these parameters that could influence) the more resistance the air has to it's passage through the barrel, thus it takes longer for the compression cylinder to dump it's contents through the transfer port and the piston to reach the end of it's stroke.
Bottom line, think of the extreme example of decocking the gun by slowly releasing the spring tension! Or jacking up your car and unloading the suspension. Would you think that this could ever hurt the springs?
I am guessing that having too much of resistance is not the same as abruptly stopping the spring before reaching it's full length either, since air is a highly compressable medium and the piston/spring system is essentially "air cushioned".
"Should I just conclude that using heavy pellets is not nearly as bad as using very light
July 3 2009, 6:50 AM
Definately!
And the verdict is still out if the heavy ones are bad AT ALL....
My practical experience with springs in various applications and my theoretical knowledge of physics is telling me that that's yet another airgunning "urban legend".
Then again, when it comes from the lips of "legends" like Hector who everybody (including me) trusts - it feels almost heretic to say otherwise. Who am I to question them?
Better wait for their responce before you start shooting heavies and then blame me
and look at results from the field. The general consensus, so far as I can glean from postings here and elsewhere, is that heavier pellets shorten spring life compared to "standard" weights.
As to the bore size VS recoil, etc, there was a couple of articles years ago in Rifle magazine about what was dubbed the "Rocket Effect". The gist of this is that a larger bore produces less recoil in cartridges where the ratio of bullet diameter to case capacity is high. (For example, .22-250) Theory is that the smaller bore produces more backthrust as the greater amount of gasses takes longer to exit, thereby producing a nozzle effect. Now, I'm not sure this can be translated to springers, but it would seem that the .22 bore would allow air to exit more quickly, both in front of and behind the pellet. Perhaps that is why the dual barreled rifles can accomodate the .22 pellets?
Anyway, don't get too caught up in how many fps can dance on the head of a pellet, so to speak. Like Chris and others say, shoot what you want - just be prepared to replace a spring earlier. And see how much more impact, etc, you get from those heavier pills. Sometimes less is more.
As far a recoil goes, you are probably correct that there are few paralels between springers and powder burners. But powder purners are the perfect example. For a given caliber and bullet weight, the fast shooting load developes more recoil than the slower. It also take more energy (powder) to get that bullet going the same speed. As for the nozzle effect - I unfortunately missed those articles. But the laws of physics say for every force, there is an equal and opposite force. That's what we feel in recoil, its essentially the push back (amazingly) of an extremely light projectile being accelerated to a phenominal speed in milliseconds. The nozzle effect probably has to do with the total time which the force is exerted and this can have an effect on the "felt" recoil - but the total energy of the system is the same. By way of crude example, you can have a 10lb bowling ball hit your sholder at 15 miles per hour when your back is firmly against a wall - It'll hurt like heck adn probably break a few things. Or you can have a 10 pound bowling ball hit your shoulder at 15 miles per hour when your standing on a pair of ice skates. When the ball hits you, you move backwards and the ball slows gradually. The total energy of the two balls is the same. The one that hit you and slowed over a longer period of time probably did not hurt as bad (well, it still broke some things - crude example as I said.)
Quote from Model 48:
I read on a CO2 forum an interesting contradiction, that CO2 pellets deliver higher velocity than lighter pellets. This again appears to defy the laws of physics if on assume that the CO2 delivers the same pressure behind the pellet regardless of pellet weight. However, there where chrony listings to support that this was true. With numerous pellet brands and guns. So what gives -
End of quote.
You have made some interesting observations.
Could it be that since the viscosity of CO2 and air is different and depends on ambient temperature and pressure, that unexpected results were observed?
With regards to other observations on spring performance and different calibres, experiments on any ONE gun can still be pretty inconclusive because its hard to put numerical values on ALL the parameters and dimensions.I have some reservations about how accurately some data can be obtained.
Assuming that the cylinder, T/port, spring and piston are untouched, as soon as the barrel is changed from a 22 to a 177, a whole new set of variables(such as coefficient of pellet friction and fluid dynamics) are introduced.
These will influence any comparisons of bore efficiency using the same power plant.
The barrel is such a fundamental part of an airgun that as soon as it is changed, even in the same calibre, the gun takes on a new character and has to be discovered again.
Its an interesting topic and good luck with your research.
Keep us posted.
D
Both of you mention variables - an you have hit the nail on the head! There's a gazillion of them. Its nearly impossible for any of us to test them independant of all the others and determine what effect each alone has. For example, change calibers and you've also changes barrel finish, friction, pellet fit, likely pellet alloy, let alone the obvious things like pellet weight.
I stand by my statement that for a given gun, regardles of the caliber barrel on it, the power plant is the same and only stores a FIXED amount of energy. Take .177 untuned, and then tuned but for the sake of this discussion lets assume we use the same spring in both. Frequently the tuned shoots faster than the untuned. Why is this if the spring (the source of the energy) is the same? it's because the tuner, throught he use of lubricants, finish of the compression chamber, fit of the pistion and other seals, and selection of pellets, etc. has MINIMIZED the LOSSES of energy in the SYSTEM, which has a FIXED amount of energy to begin with. Assuming a spring change to a lighter spring, this could NEVER result in a higher velocity (for a given pellet weight, design, barrel,etc.) unless other losses of the system are eliminated. by eliminating losses from the system it allows more energy to be transfered to the pellet, thus a higher velocity and thus more (apparent) engergy from the gun.
The discussion all started with HEAVY FOR CALIBER pellets.
Not heavy or light in absolute terms, but on a "for caliber" relative basis.
In this sense, you need to do your math with the following principles in mind:
1.- Energy is proportional to the area under the pressure/barrel travel curve.
2.- Efficiency is proportional to Expansion Ratio (volume of gases in barrel @std. cond. to total barrel volume).
Once you get those factors in you will realize that the COMBINATION of reduced efficiency between a 13.5 grain 0.177" and a 21.1 grain .22" is enough to warrant the smaller caliber gun going off the sweet spot.
Again, maybe I expressed myself incompletely, but the whole discussion started with 0.177" caliber rifle shooting 10, 11, 12, and 13 grainers. Or at least that is what I understood.
And MV is nothing on its own, it is energy what matters. If you look at guns in different calibers, you will see that the .22" will usually output more energy than the exact same gun in 0.177".
Keep up the critical eye! NO ONE is infalible and there are no airgun gods!
Thanks for your kind words and as you say, let's keep talking about this till we all understand it.
We are talking about conservation of energy here. The cocked spring with the piston in front of it represents a FIXED amount of energy. The laws of physics dictate that that you cannot create any more energy in the system than this.
Hector 's answer is :
1.- Energy is proportional to the area under the pressure/barrel travel curve.
2.- Efficiency is proportional to Expansion Ratio (volume of gases in barrel @std. cond. to total barrel volume).
one is about energy and the other about efficiency
well, well, well
warren
PS: math only wins with LOGIC mathematics
and remember "it's 30% the gun and 70% the shooter"
one thing we need to remember is we are dealing with the same power plant for both a 177 and a 22 cal example Beeman rs 2 the rifle with 2 barrels and using the same power plant. pushing different weight pellets using the same power plant does it hurt your rifle ??
... is a non negotiable foundamental law of physics (First law of thermodynamics), so of course the system as a whole - airgun, pellet and its surrounding fluids (lubricants, air) - cannot have in total more energy than the dynamic energy stored in the cocked main spring.
I will make a long list of where the energy is going the moment we pull the trigger and then try to guess which parameters are significant and measurable/can be calculated with simple formulas.
Please, excuse me as I am writing the way each thing comes in my mind, so I am pretty sure Ill forget something.
1. Heat - produced during the compression of the medium (air) and dissipated to the environment thats lost energy flowing OUT of the system. It's amount variates in relation to the resistance the air is facing while evacuating the compression chamber. VERDICT: Obviously caliber dependent but negligible and difficult to quantify.
2. Heat - produced due to friction while the mechanical system spring/piston/seal travels along it's stroke. Obviously depends on many parameters like: type, quantity, quality of lubrication (heavy tars and grease vs. light oils), bent springs, tight/loose guides, polished or not pistons/chambers/springs/guides, piston buttons, tight or loose fitting seals, etc, etc, etc.... VERDICT: Difficult to quantify but since its not caliber specific, its not something to consider for this thread.
3. Vibrations every single molecule of the rifle, shooter and surrounding air is picking up more or less kinetic energy. This parasitic energy loss is obviously closely related with all these factors mentioned on point #2, since the smoother the mechanics the less vibrations will be transmitted and lost (energy) in the surroundings. This is what you feel in your arms (Attention: Its NOT the felt recoil), the sound from the action you might hear, the barrels vibrations, your brand new expensive scope getting slowly but steadily internally trashed.
4. Heat and plastic deformation due to contact of the pellet on the barrels ID. Its amount possibly depends on the following (and not only these) factors: pellet/barrel metal alloy hardness (ductility/plasticity), finish, rifling twist rate, rifling type, lubrication or not, choked barrel or not, pellet fit (oversize, undersize), pellet type (zinc alloy, plastic skirt, multiple sealing flanges, only the skirt rides the rifling or the head too?) and last but not least THE CALIBER!
Obviously the larger the diameter, the larger the circumference of the pellet and the larger the total area in contact with the barrel. So all other things equal, the resistance that is being developed during the travel of a pellet along the barrel is must be almost proportional to the caliber according to the simple formula: Circumference=2 x x radius VERDICT: Caliber dependent and we got ourselves a rough formula.
5. Air kinetic energy the amount of energy that the mass of air is carrying while exiting the barrel behind the pellet. Depends on the mass (amount) of air that the piston is moving (non caliber specific) and the speed of the exiting air, which is probably caliber specific s the smaller the caliper the higher the accelerates. VERDICT: The formula is usual ½ x mass x speed^2, and we could assume that the speed of this air column is the same like the pellets speed at the nozzle, since its following and pushing it out the barrel. I am guessing though that its not so easy to calculate the airs mass in real life. Does the total mass move with the same speed? Or air has different speeds in various parts of the barrel. Lets just put it aside for a while
6. Pellet kinetic energy! Hopefully itll receive the largest percentage of the springs energy and of course the most important energy conversion that takes place. After all the only reason of existence for all our fine (and not so fine) air guns is this : TO LAUNCH A PELLET TOWARDS A TARGET. Formula for kinetic energy again: ½ x mass x speed^2. All of them pretty straight forward to measure if you have a chronograph. VERDICT: Since pellets of larger caliber tend to weigh more but they also chrono slower than smaller calibers when based on the same power plant, Ill dare to that kinetic energy is NOT caliber specific. Same weight same speed pellets have the same kinetic energy - at any given moment and lets not overcomplicate things with ballistic coefficients, energy retaining, etc
The higher the pellets kinetic energy the more efficient the airgun/pellet system is!
7. Aerodynamics - or simpler put: drag due to air friction. Same type of pellets have same Cd (drag coefficient), but the drag equation includes also the objects frontal area, and that area is caliber dependent squared ( x R^2). But even though projectile aerodynamics have a serious impact for long range ballistics later in flight, they can be considered pretty much negligible at this early (and short) stage of travel through the barrel.
8. Elastic/plastic deformation causing material fatigue and failure due to excess unutilized energy which returnss back to the spring/piston system. This is what happens when you dry shoot or shoot too light of a pellet. The piston simply does not manage to transfer enough of its energy to the pellet and reaches the end of its stroke with too much kinetic energy essentially slamming on the end of the compression cylinder. This bottoming out destroys/pounds seals,pistons and compression chambers. Additionally returns energy back to the spring which chatters and vibrates violently, contributing to the effects described above on point #2 and #3.
This kind of spring chatter is the one that the fellow airgunners suspect that is causing material fatigue when you are shooting too heavy pellets. The theory is correct me if I am wrong that with too heavy for the caliber pellets the air resistance the piston is facing is so big, that its like prematurely slamming on a fixed obstacle, thus returning energy (the chatter) back in the spring
What we want from our springers is the following:
To maximize the amount of the springs dymanic energy that is transferred to the pellet. This is not only just to brag that our airgun is shooting faster than others or to have more powerful hunting rifle. We are not talking absolute energy numbers here rather percentages, for example ideally at 100% efficiency a 3 joule cocked spring will result in a pellet flying out the barrel with 3 joules kinetic energy, a 20 joule to spit pellets at 20J, etc. Of course this not possible but we should try for the highest possible efficiency which is required in order to minimize wear and tear of the mechanics.
Efficiency = dynamic energy stored in spring / pellet kinetic energy
Thus
Efficiency = ½ x k x x^2 (Hookes law)/ ½ x m x v^2
Where: k is the spring constant, x is springs deflection while fully cocked, m is pellets mass, v is pellets velocity
How do we get this high efficiency?
Well with the same power plant we have a fixed amount of energy that is being supplied to the system, the only thing variates is the pellets kinetic energy and subsequently the only parameter we as shooters can really play with is the pellets mass.
Having said that, I could stop rambling here and just advice everybody to try every available pellet out there and settle for the one that develops the highest kinetic energy in your gun if you want your spring to last as much as possible as you see accuracy is optional in this study!
Ill think out loud an extreme example of two rifles of different calibers (.25 and .50) - otherwise identical shooting pellets of equal weight and similar type/shape. Obviously the .50 pellet would be light and the .25 a heavy for its caliber model.
According to point #4 the .50 pellet will need about twice the force exerted to its base in order to overcome the friction and start moving. BUT this force will be reached much sooner along the chambers pressure/time curve because double diameter results in 4 times base surface (ð x R^2) thus for a given pressure the force exerted to the pellet will be 4 time larger.
If we take this as a fact and apply Newtons Second Law: Force=mass x acceleration, we will find that the larger pellet will receive 4x more force at its base will accelerate 4 times faster in the barrel than the smaller but equally heavy one. But everybody knows this does not happen
Why? There are many theories might contribute to the real life performance. Like I said the larger pellet will develop about double the amount of drag due to friction in the barrel. Second, I am guessing that since the larger barrel has a higher internal volume, the pressure will start dropping much faster behind the pellet, as the pellet travels along the barrel.
Bottom line, the result will be similar fps @ similar grains, thus similar energy which means similar efficiency, which means similar residual fatigue on the spring.
Hope I didnt tire you unfortunately my maths are no up to the task for a more scientific analysis.
We are in fact talking about two different things- energy and efficiency! But they are also closely related and there's some dynamic thing that eludes me!!!
We'll get it sorted out here in the Dianwerk fashion!!!
I was assuming a heavy for caliber pellet (same caliber) and not interchanging them as this adds additional variables. There's no real way to compare a .177 to a .22 in front of the same power plant as you change too many variables in switching barrels (pellet design, barrel finish, pellet/barell fit, not to mention the obvious - pellet wight.)
But given a light (not too light such as to mimic no pellet) pellet vs. a heavy pellet in the same caliber (and assuming absolutely no other changes) the pellets should exit at exactyly the same energy. From the perspective of the spring, this equates to the spring slowing slower (figure that out) at the end - Or Does it? The spring may in fact come to a more abrupt stop agains a higher pressure developed by a (reletively most of the time) heavy pellet that takes a bit more to get moving. I think the answer lies somewhere in the dymanics of this if its true as has been told time and time again about springers that heavy for caliber pellets are hard on springs.
Now for the last, and most important comment to your reply - You mention efficiency. This is in fact the key to all the tuning discussions. The more of the springs energy you convert to pellet velocity, the more (apparent) energy the gun developes. The gun really has no more energy because the source of energy is contained in the compressed spring. Its just that by minimizing losses, the pellet gains more energy. Unfortunately, we have the ability to measure energy only in the speed of the pellet. The available energy in the cocked spring is the same. The amount of energy that is departed to the pellet (where we measure it) can vary from pellet to pellet and from pellet wieght to pellet wieght and from pellet design to pellet design and from pellet alloy to pellet alloy, and so on and so on. As we vary pellet design by shooting a different brand of the same weight pellet, we unknowingly change a but#-load of variables. But you are correct in the fact, and I think the answer lies in efficiency, not the magical creation of energy.
Respectfully, and still seeking the answer - Do heavier (for caliber) pellets damage your gun answer,
Model 48.
PS - I dont think anyone here is wrong, or has incorrectly reported real experience or data (see the C02 references) its just that no one has put them in terms that my pea sized and stubborn brain can comprehend!!!!!!!!!!!! I just have got it under my skin to get a satisfactoy answer to this question. Incidentally, I reported here some time ago that my 48 shot something heavy (for caliber) like a beeman silver arrow with a decided smooth cycle and satisfying thunk upon firing. Ive held off shooting them for the same fear of damage reason, and the fact that I will have to significantly adjust my scope away from "standard' springer pellet weights if I want to shoot them to point of aim (they hit high.)
While there are a lot of good points in your analyses, there are a couple of misconceptions:
Let me describe the shot cycle in energy terms:
The spring is compressed by your hand: the lever ratio is about 7 to 1. Compression force is about 40 lbs. That makes the total force compressed in the spring about 280 lbs FORCE, or 127 Kgs. or 1250 Newtons (Approx.) this is kX.
X is about 0.2 m, just for the stats, we will not use that datum.
When the piston goes forward, the temperature inside the piston raises to about 3,000 °F for a very short time, about 1 milisecond. This burns a little of the chamber oil and yes, there is MORE energy there than the one we put into the spring. It's not that it appears from nothing, it was there as chemical energy, we just transformed it into mechanical energy. That is why people hone the inside of the cylinders, to make them "hold" more fuel. If you truly want to use an airgun as a pure airgun, you will hardly get 700 fps from a gun that usually develops 900 fps. Yes, we use chemical energy in our airguns. That is why we tune them and lube them and maintain them. Most of the energy is given to the piston in the first 1/4 of it' crazy race towards the transfer port. The piston gets totally decelerated in the last 2-3 milimiters. The decelerations applied are of about 2-5,000 g's depending on the model and brand.
But the energy that got transferred to the pellet is not the spring energy, it is the combined piston's kinetic energy plus the little chemical energy of the controlled combustion. That energy gets put into the air that was scooped when the cylinder moved forward and the piston remained behind locked by the trigger. The air is just the MEDIUM through which one energy goes from one place to another, from the piston to the pellet through the transfer port.
Now, the air, at that temperature is not a gas, it's a plasma. And plasma physics are somewhat different from normal gaseous physics. Plasmas can go through small holes almost without friction. (CO2 is not a plasma, on the contrary, CO2 is "sticky", viscous. You can expect all sorts of strange things from CO2). So that is why Transfer ports have very little difference and why manufacturers can get away with using the same TP's for both calibers. They shouldn't, but they are.
But whatever the manufacturers do, they cannot ride above the laws of physics.
If the piston's energy "runs out of steam", then the total energy output will be lower than the base case. If the expansion ratio is so low that the pellet cannot absorb all the available piston's energy, then the pellet energy also goes down.
Let us take a D-48 in .22" as a base case. This is a 23-24 ft-lbs model. If you look at most published figures, those energies are obtained with pellets in the 14-15 grain category. If you take the same powerplant and connect it to an 0.177" barrel, then energies go down to 20 ft-lbs tops. If you take the same powerplant and connect it to a .25" cal. barrel, then energies ALSO go down to 18 ft-lbs in the best of cases...
The barrel length is one of the aspects that define the expansion ratio. For large guns like the 48 with quite a lot of swept volume, some barrels should be longer, but they cannot depart from the relatively standard shape and design of the gun. So, again, performances vary between calibers.
Coming back to the main and initial question: Heavy for caliber pellets fatigue the spring before medium weight pellets. Yes there is no doubt about it. I posted some time back a slow-motion film of a Kalashnikov recoil spring; and how it bounces back and forth before settling in again. This is because the Kalashnikov does not use a tight fitting guide like the ones our tuned guns use. The spring goes back and forth several times and this equates to several operations per shot. So, yes, springs fatigue earlier with heavy for caliber pellets.
If you have a good guide, then you minimize the effect.
If you have a larger caliber gun you minimize the effect.
If you keep your gun in tip-top shape you also minimize the effect, but it is there.
Now, having said that, I will repeat myself: If you gun shoots well heavy for caliber pellets, the shoot them! Be prepared to change springs every year or so if you shoot the gun often, but springs are relatively cheap.
Now, to put some perspective into the discussion: 10 grains and heavier are HEAVY FOR CALIBER 0.177"
12.5 grs. and heavier are heavy-for-caliber in .20"; 15.5 grains and heavier are heavy for caliber .22" and 22 grains are the border in .25" and all these are equivalent between themselves, they are calculated using the Sectional Density.
The other aspect is that you need to remember that, as Dimitri said, what counts is the sudden deceleration of the piston. THIS is the energy that gets transferred to the pellet (plus the little chemical energy of the oil's combustion), not the STORED energy of the spring but the kinetic energy of the piston. Which may not be the same.
If you think along these lines you will also see why a heavy piston is better to shoot heavy pellets, and/or why the dead-blow pistons have so much more energy available to give to the pellets.
In the end, the rifle is ONLY a machine. It has a sweet spot that depends on a lot of things, and YES! you SHOULD try ALL the POSSIBLE pellets! YES, Yes, Yes! ALL of them! You amy be surprised at how different one pellet of the same weight behaves when compared to another.
There are so many variables that the best thing to do is to simply look at all the published figures and come to terms with the fact that our guns will not deviate substantially from the others. We need to try all the pellets and figure out what does THAT particular gun likes or dislikes.
IMHO, the best way to tackle that task is to chrono the gun with different weight pellets; and based upon the pellet that yields maximum ENERGY, work in that region to find out WHICH of those pellets in that weight bracket are the most accurate.
"IMHO, the best way to tackle that task is to chrono the gun with different weight pellets; and based upon the pellet that yields maximum ENERGY, work in that region to find out WHICH of those pellets in that weight bracket are the most accurate."
the air gun is a platform that uses the piston, spring and other components to achieve the best output based on the weight of the pellet
and if so, then you have to shoot the air gun with different pellets weight to FIND the MAX energy level
at that MAX level the air gun is working at is't most efficent level not under or over
warren
PS: and of course accurate also
and remember "it's 30% the gun and 70% the shooter"
in my search for the answer to "do heavy pellets damage springs". I will still do some math, I will wonder at all the losses of the system, and the additional energy that dieseling provides to a pellet, not just a terible case of an overlubed gun and the additional energy from this, but the consistent additional energy from shot to shot over thousands of shots that adds energy to the system, of the diferences in the potential energy of a retained spring, and the kinetic energy of the piston which has no energy but for the potential energy in the spring minus the losses, of air becomeing a plasma and plasma physics which I've never heard of and will need to research, and of the fact that many people report shorter spring life with heavy pellets, and of the differences in springs that may have been shot only with light pellets and those only with heavy (each exclusively) and how many statistically significant tests have been run to eliminate the possibility of differences between the springs used in the tests, and the fact that those who seek out and shoot heavier pellets may just shoot more than those who buy the standard pellets,and of potential energy being converted and lost to heat in the compressed air, and of the possible difference between two same weight and same caliber pellets in the same barrel and why one shoots faster than the other, and the efficiency of the "system" which is paramount to developing velocity which is the only method by which we can measure the energy output of the system vs. the stored potential energy of the system, and of how efficiency (which is the ability to minimize losses and transfer more stored potential energy to the pellet, which is measured in velocity) has any thing to do with how a heavy pellet damages a spring, and how many of the topics discussed here (inlcuding my ramblings and side discussions) have anything to do with the answer of why a heavy pellet damages a spring, and all of this with an eye on the yet to be disproven law of conservation of energy.
I fall over exhausted, yet not disrespectfully to anyone here. Its just not yet been answered to my satisfaction to date. I will continue to study the situation and post when and if I understand it.
And lastly, I agree whole heartedly with the mantra "Find what your gun shoots well and shoot it!" Upon reflection, I imagine that very few here (myself at the front of the line)have shot a single gun enough to wear out a single spring, let along numerous springs on a single gun or multiple springs in numerous guns to begin to see a pattern. That being said, many of us that read the boards (myself at the front of the line) probably worry needlessly about damaging a spring due to heavy pellets. Shoot what it shoots well and hopefully we will ALL break a spring(s) and be able to give the data that supports if it was due to a heavy pellet or a light pellet (start that log book!).
Ok, I don't know how to explain this but i'll give it a try.Based on all the in depth previous postings, I came to the conclusion that it has to do with the deceleration of the spring.Think of this: you are on a hyway doing 140 kph like everyone else.the guy in front of you starts to slow down gradualy ,an so do you. Nothing happens, just normal ware of your brakes. Now the guy in front of you slams the brakes like there is no tomorrow! You are going to try to miss him, if you can.All the ones behind you will do the same up to a distance when they can start to stop more gradually.Chances are good of a couple of fender benders at best , or the beginning of a pile up.
Now think of those cars as being the molecules that make the spring.See where I,m going? The spring has mass, and one side of it stays stationary (It probably doesn't, but for the sake of argument lets just assume so), and the other reaches maximun velocity together with the piston. That same velocity combined with the mass of the spring will create kinetic energy within the spring.At one end being zero and max at the other.Most of that energy will go out the barrel with the pellet, but some (how much I don't have any idea) will have to be absorbed by the spring.
As I write this ,my mind wonders into trying to come up with a solution.
I think that I'm not too far from the truth (wishfull thinking) because, I just remember two cases of broken springs , that broke close to the piston.
The only thing that I can come up with as a solution ,is to take away as much mass as possible from the fast moving side of the spring.
A taper wire would be impractical or impossible , so I propose a variable pich spring with the maximun pich facing the piston.
What do you guys think?
The only thing that I can come up with as a solution ,is to take away as much mass as poss
July 8 2009, 4:45 AM
Ottok,
how is this gonna help? A lighter piston with less innertia will have an even harder time pushing the column off air that a heavy pellet creates.
Dimitris
PS unless you are refering to the theoretical scenario of a zero mass spring, with zero kinetic energy, unable to create fatigue forces against itself...
The compressed gas used instead of wire springs in the Theoben Eliminator and HW RX guns, is practically weightless and can be compressed enough to out do the most potent airgun spring.
This has been a great brain storming thread.
To get your minds really whirling, I suggest that you get a copy of Gerald Cardew's The Airgun from Trigger to Muzzle.
No airgun user who loves to tinker and experiment should be without it.
I remember reading that in a spring powered gun, some efficiency losses occur when the piston and spring rebound back just after reaching maximum compression.
They even devised a contraption to effectively halt any rearward movement of the piston, but apparently it was cumbersome and did not last long!!
While any rearward movement of the piston on rebound robs the gun of some of its efficiency, I dare say that were it not so, the piston, cylinder and spring would self destruct. Therefore perhaps a rebounding piston is not too big a price to pay for our guns'longevity.
D
I was refering to the spring and the spring alone.Sure it would make no sense to take mass away from the piston.
I thought about doing something with the spring, everything else being equal.
As for the gas ram , is out of the question, as it has no spring.The discusion was about springs ( metal springs).
About theoben, I held in my hands in 1979 a gas ram airgun, that was made in Argentina for small game hunting , so obiously it must've been made prior to that.
It was .22 cal and used extra heavy pellets made just for it.
The gas ram is been around longer that the brits will make you believe.
I found it. It was a shark rifle 5.5 mm with a barrel 455 mm long .Patented in argentina PA 213908 US patent 4.282.852
The first prototypes started in 1975 and the first sucsesfull model hit the market in 1977.Model CD-455 capable of propeling a 1.6 grams pellet at 300 m/s or more, depending on the pressure of air.
Those Theoben guns are beautifull, PERFECTLY marketed , very accurate(german barrel), great idea (probably stolen and changed enough to grant a patent) horrible trigger, poorly engineer ( compaered to Dianas) and twice the price they are worth.
Sorry , how did I get here? OH.. Yes , is all about springs.
Stay away from gas rams. Springs are a lot easier to mantain an fix.I know ,I have both.
Gas rams can be just as reliable as spring guns, and probably smoother since on the non strut types as in the RX series, the moving parts have to ride on synthetic seals.
Their "problems" start when people over pressurize them in an effort to get more piston speed and therefore hopefully increase the muzzle velocity of the pellet.
This results in burnt out seals, poor accuracy, broken scopes, loose screws...
Both gas ram and spring guns have a physical limit governed mainly by the size of the cylinder/stroke and transfer port, that ultimately establishes the gun's power regardless of the type of power driving the piston.
As a kid about 40 years ago, I recall seeing scuba divers with Italian gas rammed spear guns and boy could those things shoot.
So using the gas rams for propulsion, is not something new or inherently unreliable, if it is used within its design limitations and application.
Really, really good observations, BUT, you missed out on two things:
David.- Otto has probably made more for the understanding of the piston re-bound than anyone else I know, including the Cardews. His Dead-Blow piston works, and proved itself well. It is a much more elegant solution than the Cardews' (or any other, ABD -AntiBounceDevice-), so Otto could talk a thing or two about piston efficiency if he cared to.
You also forget that tests have proven undeniably that GasRams are LESS efficient than spring driven guns. I.E. they need more stored energy than spring guns to yield a given power output. Where´s the trick? In the peak force required to compress the Ram. Why? Because seals are inherently inefficient and Spring guns have ONE seal, but Gas Rams have at least THREE. AAMoF, it's the seal the one that is most responsible for losses (not his fault though, he does the job he is commanded to do), as it is the part the creates all the friction. A smaller, thinner, better seal is much to be preferred.
The problem with GasRams and Diana guns is that the piston locks in the stem. Not like the British versions where the trigger locks into the piston wall or into a shoe. Since the piston locks in the stem in the Dianas, the piston starts it's race into the cylinder perfectly aligned, not crooked. That is why Dianas are better piston guns than other guns. BUT it also precludes the creation of a GasRam for a Diana. Only Vortek did one many years ago and it was a dismall failure. It worked well for a few thousand shots and then broke down. I know, I had two and probably the only extant working piece is in my collection. So, until we can find a way to improve on the Vortek GasRam, we will need to stick to the Steel spring.
Otto.- more than thinking along the tapered wire spring, you could also think along the variable pitch spring. That will also put less mass where you want. BUT you need to remember that either way, there will be more stress in the sparsely populated regions than in the closely wound ones. And Stress, coupled with Fatigue, is what kills a spring.
And again, I repeat, when you use heavy for caliber pellets, For the spring it feels like taking multiple shots per pellet delivered. The spring encounters that suddenly-braking driver and decelerates suddenly, but the energy has to go somewhere and it flows BACK into the spring, re-loading it. It then goes forward to a piston that very little room to manoeuver and so, rebounds again. This goes on about 5 or 6 times till the spring's guide can dampen the whole dance.
So, shooting ONE heavy for caliber pellet feels, TO THE SPRING, as shooting 4, 5 or 6 times, therefore, fatigue and stress take their toll.
This I got from firing pins. Metal is crystalline. If you drive a firing pin forward on an empty chamber enough times, the sudden stop due to the pin's shoulder (assuming it has that design) will cause the metal to flow forward a tiny, tiny bit. The crystalline structure will compress. Enough times and the the tip will protrude and become brittle, causing breakage and primer piercing. Springs are also crystalline. Compression cycles must have some similar wear which changes the makeup of the metal in the spring. Perhaps this is why they seem to fail as they do.
Many falilures in metal parts can be traced back to improper heat treatment.
Just to see what happens, one day, I'm going to get a couple of springs and send them to get cryo treatment.They use that in many cases to toughen up steel after heat treat.It could be a waste of time , but next time I send stuff for heat treat I'll try to send a couple of springs, and just to compare , I'll send a new one and a "tired" one.
When I do ,be sure I'll let you guys know.
It would be nice to do a destructive test on those as a good comparison, maybe shoting 2 or 3 heavy pellets at once , or add some oil for heavy dieseling. Again, it may be a waste of time , but I see it as the interesting part of this hobby of ours.
I recall seeing the insides of a HW90 (gas ram gun), and the main piston had a dummy piston that was free to slide up and down the whole length inside the main piston.
I presume it was designed to deliver an anti rebound blow to the main piston.
Similar to dead blow hammers I suppose.
Gas rammed guns have a unique firing sensation and in my mind's eye, I see the firing cycle as being over a lot quicker, kind of like a flick rather than a push.
Its probably due to the higher pressures involved that fall off very rapidly, whereas a metal spring exerts less but comparably more prolonged pressure.
Its difficult to put it in words and has to be experienced.
For this reason, some find gas rams can be more difficult to master for accuracy.
Hector I agree that the higher pressures in gas rams, increase the frictional loads in the ram seals and rob it of some efficiency. I can put up with such foibles and derive great pleasure from shooting one as accurately as my ageing eyes and limbs permit!!
I used to have a Honda motorcycle that had front shock absorber springs that were wound with different pitch, meaning that the coils were more closely spaced at the ends and further apart in the mid section.
I doubt if motor cycle springs have to take as much punishment and loads as airgun springs, but perhaps this idea is worth looking at.
The piston with a central rod lends itself better to being accurately guided for maximum energy transfer to the air and to the pellet.
I recall seeing a thread here where someone asked if it was OK for the central rod to be slightly wobbly and loose on the piston.
Apart from trigger issues, I do not think a loose rod is good from an energy transfer perspective.
As is widely acknowledged, a well fitting spring guide is one of the most important modifications you can do to an air gun.
Not only does it prevent unwanted spring vibes, it also guides the piston via the piston rod accurately down the bore. Therefore the guide must also be accurately held/ located on the end plug.
Great points raised by one and all and thank you.
D
David, you are correct about that piston.Is is suposed to work as an inertia mass that will move inside stoping the rebound of the main piston.I found that it works more on a principle of cavitation( same idea as pounding on the bottom of a bottle to pop the cork out).How is that? simple, inside the piston where this dummy resides, there is very little room for it to move as freely as you would expect, and is held in place secure by the viscosity of the oil used inside the piston.Once you let the system loose , the speed of the main piston is such , that the dummy separates from the front wall where it sits , creating a vaccum in between. When it hits home, the inertia of it plus this vacum, brings it back ,slaming , and efectivelly stoping the rebound of the main piston.
I found that you can increase the efect by making a cavity inside the main piston and fill that with shot.
the gun I used for this test is my Crow magnum.The advantage is that (very time consuming) you can experiment with different amount and size of the shot.By adding SAE 20-50 with the pellets I stoped the anoing ratlle of the pelles inside when you shake the gun.No mayor difference was seen on the performance with or without the oil.
The cavitation efect, I found , is better suted for hypower, as it does not preform as efficiently with lower velocities.On the othe hand the dead blow piston performs great in all situations tested.
I still have to try this with Dianas.The candidate for that is my 350, as there is enough room in the piston to play with.I am thinking to keep the swept volume intact ,but use the spring from the 48 to gain more room inside the piston and make it considerably heavier.
All of that will take time , wich ,sadly , I don't have at the moment.
The spring rate is calculated as follows:
(WD^4 x 11500000) / (8 x NC x (OD-WD)^3)
OD=outside diameter
WD=wire diameter
NC=number of coils
now: "The power that the gun imparts to the pellet is largely dependent on the capacity of the spring to hold energy."
Energy is another word for work, and it's simply "force x distance".
on a M34 the spring is 11.5" long and if set in comes down to 11"
at 11" it has its force and distance already incorporated; with the piston, top hat and rear guide you add from 1 1/2" to 2" to the spring and that is called Pre-Load
Pre-load is what kills the spring if not done proper
all springs; being them OEM or from outside sources ie; JM are done to the proper Spring Rate for the specific Model
It is the improper pre-load that damages the spring and not the pellet weight
warren
and remember "it's 30% the gun and 70% the shooter"
David, I had a gun with a spring like you described
July 10 2009, 3:46 PM
It was a Kral Condore (CFX clone) which someone had replaced the spring in. He used an old JM model "Dulcet" which had two different windings and could be reversed to change performance. Apparently was a hot number in TX guns once upon a time.
For experimental purposes, I think that if a piston is manufactured from two or even three cylindrical sections which screw and pin together, more possibilities exist to experiment with lock time, internal profile, power output, insert sleeves, weights, recoil reduction etc.
I am thinking along the lines that if the outside diameter is always going to be the same, it will serve as a carrier for the internal parts that can be modified at will. The internal parts can be adapted to increase the weight, make it float or move independently, fill it with lead shot or whatever.
This is an area for experimentation where possibly gas rams (not the gas-strut types that one inserts instead of a spring), are more happy to lend themselves, since the pistons internal space which is normally taken up by the spring, or rod in a gas strut, can to a certain extent, be utilized to experiment with sliding weights, valves etc.
Just a thought I wanted to share...
Unfortunately , at this point in time of my life, time is rather limited to me as well and most of my ideas remain just ideas for now.
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