Radiation wrote:The problem is that the gun you referenced is an airgun.
The "captive piston" cartridges mentioned above are all power-burning firearms, I don't know where you got the airgun from?
It is more silent naturally.
That depends heavily on the airgun. If you've ever been next to one of these when fired without a silencer, it's even louder than a rimfire. The same is true of most high powered air rifles. Silencing an airgun is actually a much more difficult proposition as the pressure of the gasses is not the result of the temporary heat derived from a chemical reaction, but mechanical compression.
With a combustion based gun the only way to silence the sound is by (as you said) giving those gasses somewhere to expand before exiting the barrel OR by sopping up the heat and therefore energy of the exiting gasses either by an advanced baffling system or condensing the expanding heat on a thermally conductive surface such as steel wool etc.
As above, the captive piston design works very well for cartridge firearms, take a look at the PSS.
The heat and mechanical stresses on that thing are going to be large.
In terms of heat, I'm not too worried as it tends to dissipate fairly rapidly. Mechanically, a lightweight sabot travelling fast enough does have enough "oomph" behind it to cause serious damage so yes, a beefy unit is required. As you mentioned though, it doesn't compare to the catastrophic failure that would result if the projectile hits the barrel.
In this case, I'm fairly sure the foam keeps things centred, and I'm using multiple projectiles shotgun style, the hole is far bigger that it should be but this is for insurance purposes really, just in case the shot isn't centred.
Too big of a diameter however, and out comes the foam plug. Back to the drawing board...