I have read from this forum and other places that the ideal diabolo pellet speed should be around 850-875fps. Lower or higher speed the wind may have more influence. Higher speed also creates stability issues. This is based on my recollection but could be somewhat off.I understand crossing sound barrier would induce stability issues as things are more "chaotic" when aerodynamics transition from one model to the other. What if we shoot the pellet way above the sound speed so the pellet will travel supersonic for a long range. Will the drag be so strong that this is not practical?What if we use bullet (no skirt)? 22LR bullets are commonly shoot at 1300fps and will cross sound barrier after some distance, but I have not heard too many complaints about the instability and inaccuracy. What link did I miss here?
Can we just use a PB barrel for air rifles?
Faster bullets need different twist rates to stabalise the bullet. Slower twist rate for faster bullets, I think it is. That alters the Magnus effect that tries to pull the bullet off course.There must be some relationship between the density of lead and the speed at which it can be forced through a rifled barrel before it starts to slough off pieces of lead or even experience contact melting. I don't know what the limits are but to improve the performance, or better said to produce a pellet that will allow powder burner speeds will increase the cost of a pellet.If you want a powder burner level projectile why not buy a powder burner gun. Cheaper that way I would think.One of the chaps at our small bore club tried a few high velocity .22lr bullets. Not nearly as accurate as the sub sonic, although part of it may have something to do with the production quality of the round.
Quote from: Wolverineshooter on September 17, 2018, 04:40:27 PMCan we just use a PB barrel for air rifles?There was a thread on this very topic maybe 6 weeks ago. Lots of good discussion.
biggest prob is to get the round to the 1700 fps that would begin to make it worth while... could maybe get a 20ish grain round there on helium with a lo---ng barrel...
jmars notes above that he has had good accuracy from velocity near 1000fps. I believe Dairyboy noted similar recently. Others have noted the same. This suggests to me that the velocity "limit" often discussed for diabolo pellets may be less related to physics and more related to individual parameters of the pellet and/or barrel. Seems that if any diabolo pellet can shoot well at near 1000 fps then most any other similarly shaped projectile should be able to as well.Many ultra high velocity rifle shooters have experienced bullet failure in flight. I've seen it myself with .204 Ruger varmint bullets above 4200 fps. It can sometimes be seen through the scope as a puff of grey smoke and no impact of bullet downrange. This is commonly assumed to be related to barrel twist rate and bullet velocity-higher velocity spins the bullet faster through the same twist rate and a failure limit can be reached based on bullet design/strength.Another consideration-in firearms, faster twist rate is a factor that can raise the chamber pressure experienced. It takes more pressure to push the bullet down the barrel when twist rate is faster. Some makers of ultra high velocity PB rifles use a slower twist barrel to both avoid bullet failure from spinning at too high a rate as well as keep chamber pressures from reaching a dangerous level as quickly. You're not likely to blow up an air gun due to such factors but it is a concern in PB's for any non-factory ammunition. In air guns this would seem to be related only to a velocity decrease with faster twist rate barrels for a given volume of air released.Now put all that together applied to air guns and what have you got? I don't know but it seems like it might be interesting.
Obviously air guns work at much lower velocities. Twist rate/spin rate/velocity may all be important factors to air guns, however. I assume that assuming weight effects spin rate would be wrong. Velocity would effect spin rate, weight would not. Unless you are trying to say heavier weight pellet MEANS slower but this is not always the case with variable power level guns. Just need to be clear.
What if we use bullet (no skirt)? 22LR bullets are commonly shoot at 1300fps and will cross sound barrier after some distance, but I have not heard too many complaints about the instability and inaccuracy. What link did I miss here?
Quote from: Wolverineshooter on September 17, 2018, 02:34:33 PMWhat if we use bullet (no skirt)? 22LR bullets are commonly shoot at 1300fps and will cross sound barrier after some distance, but I have not heard too many complaints about the instability and inaccuracy. What link did I miss here?The .22 rimfire HV loads are well documented as being less accurate than the sub-sonic match ammo. They are generally sufficiently accurate for hunting, so no practical problem. When the light conditions are just right, and using a powerful scope, you can sometimes see the high velocity bullet upset as the super sonic air waves pass it.