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Air Gun Home Forum Index » Pellets/Ammo » High Velocity Pellets lose accuracy Goto page Previous  1, 2, 3, 4  Next
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PostPosted: Mon Mar 17, 2008 5:33 am Reply with quote
broommaster2000
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how do Eley Magnums do at supersonic velocities? According to their shapes I recond they'd be doing a bit better then Diabolo's.

Anyway, it might be a plan to cast and test your own pellets for such guns. With the right weight and shape you should be able to shoot beyond subsonic, right?

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PostPosted: Mon Mar 17, 2008 6:16 am Reply with quote
23ib0d0n
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Any shape slowing through the transonic barrier is buffeted by that 'pressure wave' collapse, thus is subject to upset and 'tumbling' or just makes a change from the original flight path.

When the tail of a bullet no longer rides in vacuum, that 'point first' shape isn't conducive to stable flight and will usually 'flip' tail first as drag {along with ballistic coefficients} are quite different during subsonic flight.
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PostPosted: Mon Mar 17, 2008 9:35 am Reply with quote
broommaster2000
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23ib0d0n wrote:
Any shape slowing through the transonic barrier is buffeted by that 'pressure wave' collapse, thus is subject to upset and 'tumbling' or just makes a change from the original flight path.

When the tail of a bullet no longer rides in vacuum, that 'point first' shape isn't conducive to stable flight and will usually 'flip' tail first as drag {along with ballistic coefficients} are quite different during subsonic flight.


In normal english? Mr. Green

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PostPosted: Mon Mar 17, 2008 9:55 am Reply with quote
Rogerflat
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I think he means that the H2O in the upper atmosphere enhances the lift of only departing molecules, thus producing the main characterization of any further movement in the plain of high pressure.

Sometimes you just have to word it right for people to get it.

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PostPosted: Mon Mar 17, 2008 10:37 am Reply with quote
broommaster2000
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Rogerflat wrote:
I think he means that the H2O in the upper atmosphere enhances the lift of only departing molecules, thus producing the main characterization of any further movement in the plain of high pressure.

Sometimes you just have to word it right for people to get it.


...

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PostPosted: Mon Mar 17, 2008 11:15 am Reply with quote
23ib0d0n
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This is a photograph of the supersonic wave form being compressed at the leading edge of the the nose and wing. The tail is in vacuum because of the size of the pressure deformation.

This is a round nose slug

and a pointed slug.

When the pressure wave collapses, the natural laminar flow is shaped from larger to a small point


So a pointed slug flips over at transonic velocities, to more closely match the natural laminar flow model.
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PostPosted: Mon Mar 17, 2008 11:21 am Reply with quote
broommaster2000
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That makes much more sense to me. I always need to get things pictured.

However, I don't see how this answers my question:

When the bullet shaped Eley Magnums pass the sound barrier, are they more capable to cope with the unbalance in comparison to a Diabolo, and do they remain stable in flight?

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PostPosted: Mon Mar 17, 2008 11:33 am Reply with quote
clloydhi
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Whoa! Slow down 2RCHA! You are talking apples and I am talking chickens! I am referring to the exterior ballistic profile of the bullet and why it tumbled, all a function of bullet weight(length) versus rate of spin (rifling twist). You are talking about functional reliability...and anyone who has been a student of guns knows the "Bad Ball Powder" story of the M16. Lets all stay in the same boat on this trip! But you are correct on that point.
Aloha Gang!
By the way....alloy pellets still SUCK! I think it's because the weight to length ratio requires a faster twist.

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PostPosted: Mon Mar 17, 2008 11:34 am Reply with quote
23ib0d0n
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No shape 'remains stable' when is slows through the sonic barrier.

As Alstone pointed out, computer control corrects for planes 'dropping out' of the sonic threshold. The pressure collapse itself is a major disturbance at the leading edge AND the trailing edge - at the same instant.
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PostPosted: Thu Jun 25, 2009 6:21 pm Reply with quote
donwalk
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i would think the diabolo shape would be more likely to remain stable up to supersonic/transonic speeds.

with all the weight in the front/nose of the pellet, the design makes it behave like a badmitton shuttlecock; the tail/skirt will ALWAYS follow the weight of the nose/point.

rate of twist...too much weight in the REAR...may also be a deteremining factor in stabilization.

a few years ago i purchased a .223 varmint rifle. in it's manual it cautioned against using bullets more than 55 grains as they would be unstable due to rate of twist; it had a 1:12 ratio twist rate...the old weight/length to spin surfaces, eh?

a few years back i invested in sizing dies for .177 and .20 pellets but i found it didn't really seem to make much difference in accuracy. it 'dawned' on me that the skirt expands under pressure anyway...why worry about sizing it? it's "self-sizing"...duhhh

FWIW...IMHO...i think the diabolo is the best and most stable design for air propelled projectiles traveling at speeds lower than sound. if the speed gets too slow (below 500 fps) then i think round balls or a kodiak style pellet with shallower head/shoulder angle back to the skirt and very nose heavy are a better selection as 'wobble' enters the equation.

if a diabolo pellet 'tumbles' i think there is a problem elsewhere...especially if it's shot from a rifled bore.

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PostPosted: Thu Jun 25, 2009 6:32 pm Reply with quote
fritz
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I'm pretty sure that below 500fps you wouldn't experience problems, because the pellet is still turning the same amount in relation to distance travelled as is one going 800fps. The slower projectile is taking more time to get there though, which will give wind or other things more time to affect the path of the projectile.

That is a good theory that diabolo projectiles should be more stable (especially during transsonic flight), but I think the reason modern burners use spitzer bullet designs is for the greater ballistic coefficient and other even more complex ballistic reasons.

I think that if you got an airgun barrel with a high twist rate you could effectively shoot burner bullets (given the gun is of sufficient power). Since they have the spin, the vacuum should not force them to tumble. Given the "superior" ballistics of the spitzer it should retain its velocity further downrange- giving you more power where it counts. Those faster spinning projectiles might also be affected less by wind because of their higher twist rate.

Does anyone have a .223 Daystate that they could try using burner bullets in? What is the twist rate on the Daystate? EDIT: IIRC it is designed to fire 32-40gr bullets... so the heavier .223 bullets may not stabilize properly.

Another EDIT: Someone said that "undefined laws of physics" or such can make you get keyholes with diabolos. Not always... make sure you are cleanly cutting the paper. I can get "keyhole" shaped cuts in paper from odd angles or distance where the pellet cannot cut the paper, but rather tears it.

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PostPosted: Thu Jun 25, 2009 9:04 pm Reply with quote
kanyon
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Unless yer target shooting its a non issue..

infinity...14.5gr - 1220fps
AR6.....14.5gr - near 1300fps
and I can still drop a bunny at 70+ metres..
the pellet only above the speed of sound for a short time....

Pete
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PostPosted: Thu Jun 25, 2009 9:20 pm Reply with quote
fritz
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I thought we were talking about how pellets become unstable in flight once they return to subsonic. The instability was caused by the deceleration and the vacuum collapsing.

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Pellet stability 
PostPosted: Fri Jun 26, 2009 2:56 pm Reply with quote
Griff1950
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I've shot burners of all types for 50 years or more, and the only reason that a bullet loses stability is either the wrong twist rate for the bullet weight or if it strikes something in flight. A bullet that isn't tumbling at 100 yds. won't be tumbling at 1000 yds. If the pellet is tumbling at any range, it wasn't stable when it left the barrel.
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PostPosted: Fri Jun 26, 2009 3:51 pm Reply with quote
fritz
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That is correct Griff.

For the most part. The bullet will not be stable once it goes below the speed of sound because of the vacuum pressure.

Although on paper it may become unstable, in actuality it could retain its spin, although out of its flight path (in the same general direction though). The bullet moving backwards will have a lower BC and will thusly slow quicker. All because it went decelerated below the speed of sound.

I think that may be why cartridge makers often list a "supersonic until XXyards" or something of the sort.

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High Velocity Pellets lose accuracy 
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