Not that amazing at all, really.
.45ACP is for the most part, ammo and barrel length depending, traveling slower than 1100-1150FPS.
It is, as mentioned, a bolt action. The gas has nowhere to go except into the suppressor. As you know
suppressors are designed to trap and slow the expanding gas exiting the muzzle.
You can integrally suppress just about any modern bolt gun, especially well with those that are pistol
caliber. The Marlin camp carbine thing-comes to mind. You can dive into the variety of other rifle calibers too.
.300BLK/WISPR/FRBAL, 7.62-(39)-(51), or .458SOCOM. All are equally quiet when loaded subsonic and
run in bot guns.