I really like your take on the Ammunition situation, and weapon reliability. Weapon maintenance is crucial in harsh environments and a post apocalyptic war torn former Soviet State is certainty one. Additionally you should be able to fire non subsonic rounds through suppressed weapons. The penalty could be a slightly loader muzzle report, and possible an ominous crack since the round is still breaking the sound barrier. The would cause the Zombies to go to that area, however still mask the shooter. I hate the fact that I cannot shoot full powered loads through suppressed guns as I do it all the time, and it is still very effective at masking shooter position. To piggie back off weapon reliability shooting weapons suppressed, could effect reliably depending on the weapon. IE, and AR variant rifle gets rather dirty shooting non suppressed due to their gas system, they get filthy shooting suppressed... Where and AK, M14, 249,240 ect, are slightly less prone to the additional carbon because their gas system is piston driven. In contrast, unless the developers are putting adjustable gas system in the game... sub sonic loads will generally cause non suppressed semi/automatic weapons to malfunction, as they are generally heavy bullets with less powder, therefore in the absence of a suppressor creating back pressure; they cannot cycle a weapon properly.