ballistic coefficient dataDecember 24 2009 at 3:46 PM
|Teryx (Login Teryx)|
An earlier conversation got me thinking about this. I don't see pellet manufacturers listing the ballsitic coefficients for their pellets. There is lots of data out there concerning muzzle energies from various setups. With many guns capable of reaching out 100 yards, there could be huge differences in terminal energy depending on pellet design. While something like a Predator and a Silver Bear might seem comparable at the muzzle, what about at 50 yards? 100 yards? Maybe pellet choice makes more difference than you think.
Does anyone know of a database that contains BC values for common pellets?
Steve in NC
You're right. Pellet BC does make a huge difference in...
|December 24 2009, 3:57 PM |
...not only energy retention, (what's possibly even more important) but also real-world accuracy (e.g., resistance to wind drift). Pellet BC can vary from one type to another by a factor of 4 to 1.
This database complied by Patrick H. contains a few typos and blank spaces, but is still one of the best available: http://www.airgunexpo.com/airgundb/pellet.cfm
Meanwhile, the one and only pellet manufacturer that publishes velocity retention data (from which BC can be easily calculated) is poor old downtrodden and much-derided Gamo.
Nobody else - not even the much hyped brands.
WOW worse than I expected!
|December 24 2009, 4:12 PM |
Or better depending on how you look at it. That's a great database. It really shows the folly of choosing a pellet based on how cool or wicked it looks. At 10 meters who cares, but at hunting distances you can lose much of your guns potential with the wrong choice of pellet. VERY interesting!
I'll admit, I'm guilty of Gamo deriding
Gamo ... if this is a transcription of Gamo's BC data
|December 24 2009, 6:50 PM |
then its value is extremely suspect to say the least:
Gamo Hunter 15.30 Pointed 0.220
Gamo Magnum 15.60 0.220
Gamo Master Point 16.20 0.220
Gamo Match 14.10 Wadcutter 0.220
Maybe the typewriter had the stutters?
Best wishes for The Season and Kind regards, Harry.
Have to use the plug-in calculator...
|December 24 2009, 6:55 PM |
Steve in NC
Yup. And when you do, you get...
|December 24 2009, 10:36 PM |
|This message has been edited by pneuguy on Dec 24, 2009 10:37 PM|
thanks...nice to see.
|December 25 2009, 1:57 AM |
Haven't tested those pellets for BC, but the match WC's and .177 ball seem a bit too high... and the TS10 and TS 22 kind of low (but those pellet's suck so bad in anything I've shot, who cares?).
Gamo has been and still is making two .25 pellets...if their other calibers are a guide, the Hunter should be at least acceptable in accuracy, and if they could keep the pellet cost as proportional to the other caliber Hunters, believe they'd sell. As they already make them, just need to get them from point A to point B.
|This message has been edited by gubb33ps on Dec 25, 2009 2:16 AM|
Steve in NC
I agree. Gamo's number for the .177 ball is 50% higher than...
|December 25 2009, 10:13 AM |
...my experience with round shot, and some of the other numbers look screwy as well. Maybe Gamo's test range is on a mountaintop somewhere?
However, the fact remains that Gamo is unique in publishing any data for their pellets at all. So just for fun I converted their numbers to BCs with a spreadsheet.
Thanks Steve ........ and it clearly shows
|December 25 2009, 5:27 PM |
why the .22s don't cut the mustard in the real world.
The reason for companies not publishing is probably because BC varies so much from one to another rifle.
Merry Christmas .. Kind regards, Harry.
The trouble is...
|December 24 2009, 4:49 PM |
BC will vary many times between different rifles shooting the same pellets from the same tin. Even if you take 2 of the same model of rifle and grab pellets from the exact same tin and shoot them out of both of those rifles, often they will yield different BC data. So there is obviously more going on here to it, possibly due to slight differences in barrels, slight power plant differences, etc...
Folks don't want to hear that...
|December 24 2009, 6:31 PM |
..it's just so easy to look it up on the chart and believe that's what you're going to get; why complicate it with reality?
Usually not all that far off, but on occasions will find that there is a whole lot more drop than the calculations indicate (and if you put a chronograph down range, may find it's a lot slower than predicted). One good indication of a pellet that's unhappy (and will give a lower than expected BC) seems to be to check vel. variations at the muzzle, then check again out at 20 or 25yards. IF you were getting 10 shot strings with 5 or 10fps variation at the muzzle, but find 20-25 fps variation at 20yards, then the pellet is adding some motions besides the predicted straight flight into the equation.
The good news is that when a rifle shoots way off the predicted BC of that pellet, the accuracy usually suxs and you'd not want to use that pellet anyway.
Good points Robert
|December 24 2009, 9:24 PM |
I do the same with my rifles. Once I find its 'favorite' top 2 or 3 pellets, i'll chrony them at the muzzle, at 25 yrds and again at 50 yrds as well as shoot groups at various ranges. I'll let a combination of accuracy, BC, and smoothest shot cycle(least hold sensitivity) determine the numero uno.
I haven't read where anyone said
|December 24 2009, 11:01 PM |
That they were taking the numbers as gospel. Unless they are a pure fabrication they should serve as at least as a rough basis for comparison.
I wish it were that easy man
|December 25 2009, 1:40 AM |
the numbers are just off so much, so many times that wouldn't you rather test your own rifle with it's own favorite and then you'll know for sure? A couple hundredths on a BC can mean a lot on a long range shot. It's the same thing with pellet trajectory in a software program like chairgun they are indeed fun to play around with on a cold, rainy or snowy day when you can't get outside to shoot. But your own results vary and if it's you putting lead on your FT winning shot or a rabbits head, it's better if you know for sure, a rough estimate is useless if you miss the shot or injure the quarry.
Just trying to help here, i've been down that road more than twice with BC charts, software programs, etc... I would just take those 'references' with a grain of salt as compared to what really happens when you shoot your rifle.
Steve in NC
What might be more helpful (and would certainly be more interesting)...
|December 25 2009, 9:51 AM |
...would be for you to post some of your personal BC measurements, for comparison.
Know it wasn't directed at me...
|December 25 2009, 10:56 AM |
but thought i'd give an idea of the contortions you'd go through.
We make it sound easy, but it's certainly not.
Ideal would be to have two working chronographs set at measured (exactly measured) distances, lined up for each shot to give an accurate reading. What you'll find is that each individual shot gives a different BC, usually not a drastic differences, but a measrueable one.
1. Damned few of us have two working chronogrpahs. As mentioned before, an embarrassingly large number of us have two chronographs, a good one and and a dead one that got shot... and many of the ones that got shot, got that way from putting it far down range for BC tests.
2. At short ranges, small errors in vel. readings produce surprisingly large changed in BC.
What most of us do have is one working chronograph. To use just one, need to work by averages. Take a pile of readings at one range, and a pile at another, and figure the average overall BC. Like any average, it may not reflect the true BC of any individual shot.
The other odd thing is that fast pellets slow down quicker than slow ones, which means that BC tends to change with distance. A pellet launched at 1030fps may earn a BC of .025 over the first 50 yards, then earn .03 over the next 25 yards.
Got to testing a Sumatra 5mm. Could toss the 23gr. EJ pellets to 1030fps. Used the one-chronograph-for-average type of testing.
2 yards: 1030fps
25 yards: 913fps
BUT there was a 10fps varaion in the strings used for testing. So call it 1035-1025 at 2yards and 918-908 at 25 yards. Pairing up the best and best of those averages gives a .0276 and the worst-to-wrost gives a .0232.averaged it comes out to .0254, which is close enough to .025.
Slowed the rifle down to 825fps with those 23gr. EJ's (which will keep most 14.3gr. pellets under the speed of sound):
2 yards: 825fps
Because pellets tend to change BC as they lose speed (and really change them for the worst if they start to "wobble" of "spiral"), would be better to test over a long distance...50 or 60 yards... or two test twice, once at 0-15 and again at 25 - 50yards to get an idea of how they change with vel. decay.
What I suspect, even with super accurate pellets, is that they all "wobble" a bit right out the muzzle; that blast of air that powered them over takes them right off the muzzle, and they tend to wobble a little bit. good pellets straighten out quickly, but suspect they lose more speed in that first few feet of travel than we suspect. So for all my personal use, have taken to only testing vel. at 5 yards.
OR... can just read the numbers on a chart and take them as BC-law.
|This message has been edited by gubb33ps on Dec 25, 2009 11:02 AM|
Robert, you nailed it again! nt.
|December 25 2009, 11:27 AM |
Steve in NC
Good example, Robert. Let's explore it for a minute.
|December 25 2009, 11:50 AM |
Suppose one took that BC = .03 you found for the EJs at MV = 825fps and (erroneously) used it to calculate a 1030fps trajectory.
At 50yds, the calculated drop (of course) would underestimate reality because the estimated rate of velocity loss would be 20% less than reality. An interesting question to ask is: How big would the actual error be.
The actual error (real vs calculated drop) would be 5.02" - 4.85" = 0.17" = 0.3MOA = (slightly more than) one typical scope turret click (1/4MOA = .13").
Actually...I kind of gave up.
|December 25 2009, 8:35 PM |
Find that shooting them, finding their real-world drop at various ranges does me more good. Can make a pretty good prediction of drop at longer ranges once you know the real-world drop at 25, 50, and 75 yards.
but like you mentioned, the real difference betwen .025 and .03 is just lost in all the other factors... it's not an amount of difference you can really put to use.
|December 25 2009, 11:18 AM |
Here are the BC's for the 3 top performing pellets for my .177 caliber R9. The R9 was/still is in stock form. After sampling several pellets, these were chosen based on the fact that they provided the absolute best accuracy in my gun compared to all the others.
Chrony was then used at the muzzle, 25 yrds and 50 yrds to determine muzzle velocity and energy, terminal velocities and energies and BC's of each pellet. Since all of this testing, I choose FTS's as the best pellet because they rival JSB Express as the tightest grouping pellet (0.32" 5 shot grouping at 40 yrds and 0.5" 5 shot grouping at 50 yrds, they provide the smoothest shot cycle in my gun and have almost the exact same trajectory at 40 and 50 yrds as do the lighter JSB Express 7.9g)
Pellet muzzle 25yrds 50yrds BC
JSB Express 7.9 879 avg 848 687 0.0242
FTS's 8.6 832 avg 801 656 0.0255
Kodiaks 10.6 766 avg 743 633 0.0318
I have other guns, such as the HW50S, R7, TX200, HW97K all of which shoot these pellets at much different BC's. Some shoot the Express with a lousy 0.019, others at 0.027. Same goes for all the others, they are different in each rifle I own.
Hope this helps.