Subsonic?
Bit of a novice question but why do people generally try and keep air rifle pellets subsonic?
Thanks
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It can be done, but it will require different rifling. AG bbl’s have different rifling since much of the stability comes from the skirt of the pellet. Similar to the fletching on an arrow.
You can use a .22 Long rifle BBl. and use powder burner slugs in it. This is how the 80 FPE Air Ranger works. And it works well in a gun able to provide the “Push” to gain the velocity needed to stabilize the heaver solid projectiles. ( The Air Ranger fires a .223 solid bullet. Not a pellet)
There are other ways. A Sabot for instance in a .25 or .30 made for a powder burner that enables it to shoot a .223 varmint bullet is available. These can be used in a .25 or .30 Ag bbl as well. However, a twist rate that is able to stabilize the projectile is still necessary. The is an additional problem with this system. .223 bullets with their superior BC are jacketed varmint bullets. They are designed to violently expand at high velocity. Much higher than what we can accomplish with our Air Guns. They need velocity in the range or 2500 at the very low end, to as much as 3000+ t properly expand, and do the indented damage to be worth while. It is an expensive way to go, with very un-worthwhile results in our AG’s.
One quick fix, and one that is gaining in popularity is switching from a .22 in a AG. to .25 or higher. The projectiles are heavier, and have a better BC. The Pellets are better on both counts. But more importantly, these Bbl. are in many cased able to fire solid slugs very well. Such as the ones offered by Jerry here on the Forum.
Many have built special AG’s in .25, .30, 9mm, .45, and .50 for this very reason.
So yes, it works. It just takes a little work and planning! (And Money) 😯 😀
These heavy slugs are for fpe, not fps, however, the same works for the smaller calibres. In .22, and .22 it very possible to have high velocity, and a very good BC. If I ever get this move over with, I have a lot of playing planned! There are plenty of used .22 rim fire bbl’s out there.
With the simplicity of our AF guns, and the power they can produce, there is no reason why we can’t push the envelope a lot!!!
Mike
I was just reading about how a standard air rifles barrel “twist rate” is insufficient for supersonic shots. I also found a page explaining about the aerodynamics involved.
This is all looking like lots of custom work and way past what I am capable of. O well it was a nice thought anyhow.
I’m not sure which barrel would work better or not but…
Since the projectile doesn’t get it’s behind burnt by the hot gasses of the powder being exploded, an air gun would be better for tail shape testing and ‘alternative’ shapes.
The only issues is that it takes considerable effort and development to make pellets shaped correctly. So basically you would be spending lots of time making dies and finding that they don’t work.
Accurate pellets are shaped by forming lead wire into a blank (called swaging), they are not cast like PB bullets.
So if you did make a bunch of cast pellets and they worked you would have to make sure they worked as a swaged projectile if you wanted to make a lot of them easily and consistently.
Or you could get a hold of Jerry and he can explain everything! 😆
WOW thank you all again there is some great information there. I see its the changing of pressures and forming of shock wave moving across the pellet. So some shapes would be significantly less effected than others.
Lets take it a step further and say ok we are going to try and make a AF gun fire supersonic shots as effectively as possible. What would you think may be a good barrel and pellet combination to try? This is not to say it would work well but just for the fun of trying.
A demonstration of the pressure wave at Mach1, although I remember this clip had sound once and I can’t find it, dammit….
If the pellet is over the SOS (speed of sound) when it exits the barrel the air resistance tends to upset the projectile at the muzzle (thus the crack as it enters the air at the SOS).
Aerodynamics above the SOS are different than under the SOS. Certain shapes are inherently unstable the whole time they are in the range from USOL (under the speed of light) to the SOS. This means that even though the projectile is launched and stabilized from the barrel at the SOS it will begin to wobble the instant the bore is not holding it in place. Most (if not all) air gun pellets don’t like being above the SOS.
Even above SOS stabilized projectiles have to deal with the pressure wave at the transition between USOS speeds and ASOS speeds. This is the same pressure wave that sent many a test plane out of control and the very same wave that makes the cool condensation clouds when breaking the sound barrier…
The same or similar pressure wave is present when passing back under the SOS.
The boat tail projectile was developed to aid the pressure wave’s ability to slide nicely off the back end of the bullet and neatly close the projectile’s turbulence path.
😕
So if the pellet was well over the speed of sound before it left the barrel
it would be stable until it slowed back down to the transonic speeds? So lets say you some how got 150lbft behind a .22 Eunjin it would travel true and with very little drop for around 100yard and would not start to get unpredictable until after that when it went subsonic?
The de- stabalising happens as the pellets PASSES THROUGH the barrier, and again as it slows back to subsonic.
Thank you Akula that is very interesting. So does that mean there are some pellets that would work at supersonic speeds? Something like a Prometheus Piledrive perhaps?
Zilog; Skirted pellets become unstable at supersonic speeds. AKULA
Thanks synopsys. Can you tell me why this is so? Just interested in the physics of it all. I am struggling to work out why it works for a powder gun yet not a air gun?
Stability… 😉
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I’ve just noticed that H-N of Germany (The maker of the Baracuda and what we call the Kodiak here,) is making a new bullet shaped pellet. It’s called the Rabbit Magnum II. It is over 15 gr. in 177! They don’t have the weight in .22 yet, but it looks like it is going to be available in 200 count tins. Hope we can get them here in the States. A .25 would be Great! 😀
Mike