As you (hopefully) know, a gun suppressor doesn’t completely eliminate the sound created by a firing gun. Instead, it suppresses the noise significantly by capturing and slowly releasing the rapidly expanding gases used to propel a bullet out of the gun barrel. When firing a gun, the gunpowder in the bullet casing ignites, creating an immense amount of pressure. This pressure propels the bullet down the barrel of the gun, pushing the round at incredible speeds. When the bullet exits the barrel, the pressure is released and an extremely loud noise is produced. What a suppressor does is provide a larger space for the pressure and hot gases to expand after exiting the barrel. The gases expand as they are heated when the gun fires, but the suppressor traps and slowly releases this gas, resulting in a much quieter shot. Other aspects of a suppressor that help to mute sound include the science of heat transfer and metallurgy.
But for the Soviet Union, the conventional form of suppressors bolted onto the gun was simply not enough. Some bright spark decided to reinvent the wheel. He looked at the usual barrel silencer and figured they're such crap because it doesn't make much sense to try to muffle the bang at the barrel's end, since it happens all the way back, as the compressed gunpowder explodes and the resulting gas violently expands. So he went and designed a fancy bullet case which trapped the gases inside itself, so it's actually more appropriate to say the technology is silent ammon rather than silent guns, the latter of which was designed after the former. They also were designed to minimize the secondary noise of that is the clang of moving parts, so it became inaudible beyond a few meters. Further, the third and last source of noise, case ejection, was wholly sidestepped by keeping the spent, gas-filled cases trapped in the gun itself, which further adds to the stealth. Add the complete lack of a muzzle flash, and it's as stealthy as it gets.
The downside is that it loses power and has lowered effective range, but with such a stealthy weapon, distance wasn't supposed to be a factor for the user. It's also, unsurprisingly, more expensive to manufacture than common ammo.
The prototype was named SP-1. That and SP-2 saw use only in Bond-style specialty guns, like the infamous cigarette case, the TKB-506 and TKB-506A. Later on, some different group ceated the PZ/PZA/PZAM round line, much bigger because they were intended to be usePost too long. Click here to view the full text.