Russian SP4

[no_op]

Below is a interesting piston driven cartridge that reduces noise signature by containing high pressure gases within the cartridge itself.

http://thebulletforum.com/showthread.php?76-The-PSS-silent-self-loading-pistol

Any thoughts on the legality of this round? Would the ATF treat each round as a suppressor?

[Big D]

Sim rounds work the same way. That's all I got.

[MontClaire]

Yep it's PSM alright. You can still find them on gun broker.

[no_op]

I checked out the SIM rounds and they do use a very similar concept.
Here is another more informative diagram:

[no_op]

Caliber is 7.62