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Pellet design...Tube pellets ... Experiment # 1 ...

April 25 2010 at 9:17 AM

Yrrah  (Login Yrrah)
YFOT

"Pellet design...What would happen if."... The question was asked (bottom of page)http://www.network54.com/Forum/79537/message/1272120796/Pellet+design...What+would+happen+if.....

First question: Will a tube pellet shoot and group?
I have last night returned home from the bush, read this this morning, and as LD and I had discussed this some years ago, I did a pilot study for Ron.

Only had 15 yards here today but here is the result.
Three .22 cal Predator pellets had their polymer tips removes and then they were hand drilled thus:

Predator pellet and with tip removed -

[IMG][linked image][/IMG]

Pellet drilled with felt cleaning pellet wad for sealing the bore to drive the pellet through the barrel -

[IMG][linked image][/IMG]

A group of three de-tipped Predators were shot into the lower group one hole and one drilled pellet with wad follower was shot - top hole in the POA -

[IMG][linked image][/IMG]

A second drilled "tube" pellet was shot touching the first -

[IMG][linked image][/IMG]

A third drilled pellet was shot to form a 3 shot "group of "tube" pellets -

[IMG][linked image][/IMG]

The group formed a tad higher than the untreated pellets which may or may not be because of diminished weight. The hand drilling was not perfectly centred so some improvement could be anticipated. But there is little indication of yaw.

Shot from sitting on the ground with a rest on a chair. BSA Hornet (Bowkett) .22 cal shooting at around 890 fps when last tested with JSB 15.9 gr Exacts. MV would be similar with the untreated de-pointed Predators but unknown with the drilled "tube" pellets + felt chaser. The felt cleaning pellets landed on the ground about half way to the target.

So, the first answer is that a pellet with a hole through it can be shot to a tight group at 15 yards from a less than "benched" shooting position. They appear to stabilize well.
These were the only shots taken and are not selected from a number.

Make of it what you will Ron and all, but it is interesting and I shall extend the test range when possible. ... I may even do a "Myna bird damage comparison test" when opportunity prevails.
Will they cut a neat hole? Turn sideways? Expand? Only testing will tell.
Hope this is of some interest ... Kind regards, Yrrah.



 
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(Login pneuguy)

Fun stuff! Thanks, Harry. Question: What size drill did you use? Looks like ~2mm.

April 25 2010, 10:07 AM 

That would make the area of the hole ~(2/5.5)^2 = 1/7th of the total frontal area of the 5.5mm pellet.

Close?

Steve

 
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Yrrah
(Login Yrrah)
YFOT

Sorry Steve I have been writing something else.

April 25 2010, 10:40 AM 

Yes - 2.00 mm. I can get a 2.5 mm drill through without exiting the side of the narrow neck of the Predators. Maybe I'll give that a try tomorrow. .... Kind regards, Harry.

 
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(Login gubb33ps)
YF

Good post...nothing like direct experimentation.

April 25 2010, 10:19 AM 

Was worried that the pusher would get trapped in the hollow base and not fall away cleanly every time. Having some shots with the pusher clinging on for 10 yards while others let go of it at 2 yards didn't seem productive, but evidently the felt cleaning pellets don't self-jam themselves into the base. Was thinking about drilling some 25cal pellets and using an AirSoft ball (about 24 cal) as a pusher, hoping to avoid that cling-on effect.

Years ago, PMC sold tubular copper handgun ammo based on Flatau's design (believe they ended up paying a royalty)... UltraMag?,,, used a plastic pusher that fell away, leaving a copper .38 or .44 tube spinning towards the target. Didn't measure it, but the tunnel though these bullets looked to be somewhere between 5.5mm and 6mm. Do know they were fast (being all copper, were light) and also know that that plastic pushier base would fall away early enough and had enough energy to totally wreck a chronograph screen.


 
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Yrrah
(Login Yrrah)
YFOT

I used the same felt wad for all three shots, the one in the pic Robert.

April 25 2010, 10:57 AM 

Yes, a bit of fun and I agree. We can muse over lots of things and be dead wrong.
We'll see if they hold up at 25 yards, if so I'll get more interested and do some longer range tests at the farm in a week's time when we get up there. I was sufficiently surprised at the result to scheme on a Myna ambush with post mort happy.gif ... Kind regards, Harry.

 
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(Login gubb33ps)
YF

Think I'll still try the plastic BB

April 25 2010, 11:32 AM 

Know that pellet bases do "bump up" when kicked in the rump with 3K air, so am thinking a hard pusher might still let the base get some of that force.

 
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(Login Jonnie001)
YF

Re: Good post...nothing like direct experimentation.

April 25 2010, 7:31 PM 

I read an article years ago about these armor piercing rounds called "cyclones" They were supposedly used by ATFE agents on the branch davidian raid. They were like the PMC round, in that they were tubular, but made from steel, with copper guilding, and serrations on the front part of the tube. I tried a web search (yahoo) but didn't come up with anything useful.
Maybe somebody else read the same article, and has more info.

 
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RedFeather
(Login RedFeather)
YFOT

Did you get a chance to read the old news article I posted there?

April 25 2010, 10:31 AM 

I didn't realize this idea was quite that old, being familiar with the recent tube bullets. Now, how do these penetrate in test media? The old professor back in 1893 reported reduced penetration, hence the military losing interest in them.


 
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Yrrah
(Login Yrrah)
YFOT

I used a lead plate back-stop RF ...

April 25 2010, 10:49 AM 

They compacted onto it "point" on and flatted. Will shoot some into pine boards tomorrow maybe. It's 12:45 am now and I drove 750 kms yesterday so must hit the hay soon. Just stayed up to show a token response now ...
Big day in OZ today - Anzac Day ... Kind regards, Harry.

 
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RedFeather
(Login RedFeather)
YFOT

But I want instant gratification!

April 25 2010, 10:58 AM 

Thanks. I certainly didn't mean for you to haul out the gun, etc, right away. Just maybe next time if you decided to try another batch. This discussion sort of reminds me of the early French bullet experiments by Minie. Got any balsa wood plugs, etc? What's old is new, again deparment.


 
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Ron
(Login oo7fuzz)
YF

A very informative experiment indeed, Harry

April 25 2010, 12:36 PM 

I'm glad someone as dilligent as yourself saw fit to give er a whirl.


 
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Herb1836
(Login Herb1836)
YF

Nice alteration - but shot'em backwards?

April 25 2010, 12:52 PM 

Harry,

If you have the time, I wonder how shooting them backwards would compare to the usual position. Loaded "backwards," the flange would seem to act more like a funnel forcing more air through the center of the pellet. It might help to ream out the "front" hole where the plastic tip was removed to the diameter of inner lead ring. That way a sort of venturi rocket engine throat would be created.

I'd guess that such pellets would hit higher downrange for several reasons. First drag would be reduced. Second they have slightly less weight so a higher muzzle velocity.

Fantastic experiment Harry.

Herb

 
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Charles Mellon
(Login bil601)
YF

drag

April 25 2010, 1:29 PM 

I think you need to get rid of the pinched waist in front of the skirt to reduce drag. By drilling a hole in a pellet it seems you have another drag area inside the pellet. I think you have to go with the way it was designed the first time. With an airfoil shape inside & out. While a venturi will increase air speed it wont create thrust. You cant get free energy. The higher air speed comes from the high pressure in front of the pellet. You want to get rid of the pressure in front.

 
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Ron
(Login oo7fuzz)
YF

The original post was to modify an existing diabolo pellet

April 25 2010, 3:17 PM 

While drilling a hole thru may not be as efficient as a tube geometry, the hole will greatly reduce frontal effect. But as with the diabolo, the hole thru will nagate the low pressure area behind the pellet which is also much drag.

The flared skirt design is nothing more than a spoiler is to an automobile. Which will not rid the fast moving air from forming a low pressure pocket directly behind it but manages it as best it can and shifts the stream farther back much as the boat tail geometry would.

IMHO the basic airgun projectile velocities cannot pack (compress) more air into the nose of the pellet where expansion (speed of sound)of said air on exit could not keep up with the compression side of the equation. So would the restriction you speak of really be present?


Remember, that when air passes around a corner or thru a restriction, its velocity must increase. Also that velocity continues down stream for a ways.

At even lower velocities of air, ram stacks used on aspirated internal combustion engines seem to work.

 
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(Login bil601)
YF

Thrust

April 25 2010, 4:38 PM 

The pellet leaves the barrel with as much energy as its going to have. The air moving past it or through it can not add thrust or energy to it. You cant get more energy from a venturi then is put into it. You can only get less because of drag. The pellet cant make its own thrust. The skirt creates drag just as a wing on a car does. If you look at the picture you will see the air moving smoothly over the nose. That is laminar flow. The areas where the air tumbles is drag. You may have reduced drag by drilling a hole. Or you may have made it worse by adding drag to the inside. There was no drag over the nose before the hole. [linked image]

 
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Yrrah
(Login Yrrah)
YFOT

I may shoot these things over a chronograph and compute

April 25 2010, 6:29 PM 

a Cd now that I see them grouping well enough not to "shoot the Chrony". That may answer the drag question Charles.

Do you think they will nose into the wind as a normal pellet?
Another question would be: will they be more susceptible to spin induced drift than the mother pellet? ..... Kind regards, Harry.




 
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(Login bil601)
YF

Spin

April 25 2010, 6:47 PM 

I am wondering if they will try to fly like a wing would. Or like a ball does when you put a spin on it. Now that the wieght is on the outside it may act like a gyro always trying to right itself. Which would mean it couldnt tumble. This design has already been proved to have 4 times less drag then the best bullet design. A practical working pellet would be awsome for long range target. The 38 pistol ammo they made hit 1800 fps with very little recoil. Thats almost double the vel.

 
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Yrrah
(Login Yrrah)
YFOT

Early cancellation of yaw would certainly flatten trajectory to some degree.

April 25 2010, 6:51 PM 

More research funding money required happy.gifhappy.gifhappy.gif .... Kind regards, Harry.

 
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Ron
(Login oo7fuzz)
YF

I didn;t imply that the pellet would gain velocity.

April 25 2010, 6:45 PM 

The increased velocity after the restriction is a natural function only. Which reconciles the air flow with the ambient air.

And yes, I see the laminar flow around the dome of the pellet. But that is only in relation to the pellet surface. I also notice the abrupt directional change in the smoke streams and even the resulting compression. That is drag.

So why not the wad cutter. It has less surface area than the domed geometry. Right? So then increased surface area is not always a culprit. Where a tad more stratigically placed surface area can nagate much greater woes.
[linked image]

 
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Yrrah
(Login Yrrah)
YFOT

Reduced pressure gradient from front to rear could be a positive goal.

April 25 2010, 6:47 PM 

May a tube geometry be devised to do this?
If so, then the trade off may be between the result of that when compared to any increase in drag introduced by the increased surface "wetted" area.... Kind regards, Harry.

 
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(Login bigbore)
YFOT

Harry, have any of the old Benjamim cylindricals?nt

April 25 2010, 3:46 PM 



[linked image]

 
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Yrrah
(Login Yrrah)
YFOT

Yes Lon, I have a number of the red tins with white lids

April 25 2010, 6:19 PM 

and also a number of the last old cylindricals that came in the yellow plastic boxes. Some years ago I did an extensive in-depth comparison of 25 yard accuracy/ group testing with them and a number of the older 50s pellets from various other coloured tins. The best were the Red tin kind but none came close to the precision/ accuracy of the Crosman Premiers or Kodiaks or H&N FTT; and the JSBs are now arguably the best ever.

The BC of the old cylindricals was not great and was lower than Crosman Premiers (die #1). The anticipated high BC was negated by the fact that those pellets don't stabilize their yaw early enough thus have more drag than they would otherwise. ...

What did you have in mind for them? ... Kind regards, Harry.

 
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(Login bigbore)
YFOT

Drilling them out...

April 25 2010, 10:05 PM 

they would best approximate a true cylinder; no shuttlecock aerodynamics.

[linked image]

 
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(Login MarinoJ)
YC

I would think that with more surface area

April 25 2010, 5:51 PM 

you'd have more drag. But what do I know.

 
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Yrrah
(Login Yrrah)
YFOT

That was my gut feeling some years ago when LD and I had an exchange to the question

April 25 2010, 6:33 PM 

which he posed at the time. However a BC/ Cd test may answer the question. ... Kind regards, Harry.

 
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(Login bil601)
YF

Flow & shape

April 25 2010, 6:36 PM 

If you give it a better shape you will have better flow. The benifit of better flow will outway the parasite drag from the additional surface area. You have to remember the pellet is moving, not the air. The air is just trying to get around it. Also the air coming through the venturi affect from the hole is not moving backward. It is just flowing through the hole. In fact that air is being dragged forward with the pellet. It does not act as thrust.

 
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(Login DanBollinger)
YF

It is relative.

April 25 2010, 6:42 PM 

"You have to remember the pellet is moving, not the air." It doesn't matter to the pellet, which is what we are concerned about. The pellet "sees" air rushing past it and responds accordingly.

If what you say is true, that there is a difference between which is stationary, the pellet or the air, then that means that all the wind tunnels in the world don't work.

Dan

 
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(Login bil601)
YF

In this case

April 25 2010, 7:01 PM 

The air is not rushing past the pellet. The pellet is rushing through the air. The air is not moving unless the is a wind. The air is flowing around the pellet. They use wind tunnels because its easier to get data from a stationay object with air moving over it. A round nose is better than flat. Spitzer is better then that. Spitzer boat tail is better then that. Clean flow & reduced frontal area. You get both with a hole in the middle with good shape inside & out. Thats what the original design was.

 
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(Login DanBollinger)
YF

Yeah. Right. Sure.

April 25 2010, 7:45 PM 

Here is what Wikipedia says on the topic. If you don't like what they say, don't complain to me, go to the Wikipedia page on wind tunnels and set them straight:

"The wind tunnel was envisioned as a means of reversing the usual paradigm: THE SAME EFFECT WOULD BE OBTAINED IF THE AIRCRAFT STOOD STILL AND THE AIR MOVED AT SPEED PAST IT."

http://en.wikipedia.org/wiki/Wind_tunnel


 
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Ron
(Login oo7fuzz)
YF

Yes, If you nail a goose's feet to the floor

April 25 2010, 7:55 PM 

of a wind tunnel and turn on the fan the goose will want to fly in spite of the predicament he is in.

 
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(Login bil601)
YF

thats what I said

April 25 2010, 8:33 PM 

My response was to the post that suggested the venturi effect was producing some kind of thrust. If the pellet is moving there can be no thrust of ant kind from the air flowing throught the hole. While the air does flow over the pellet the same as a wind tunnel. It is does not act the same. The pellet is moving forward which means some of the air is being pulled along forward with the pellet as a result of drag. In a wind tunnel the energy is in the air causing the flow . With a shot pellet the energy is in the pellet.

 
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