30 cal or larger caliber at 1,000 fps from a locked breach through a quality can is quiet.
I have shot a 30-30 pushing a 175 gr bullet at 1,000 fps using fast burning pistol powder. When you shoot it, you think it was a misfire and it did not go off. If a custom 1 in 7 30 cal barrel was cheap, shooting a 250 gr bullet would be no louder, but would hit much harder.
There are other combos that work better and you can bet the special forces had stuff supplied to then that was top notch.
Thanks. I am sure they had special things just for that. Just curious if anyone had experience and knew. I don't reload and am not familiar with ballistics. I just know what is available to us peons.