both of my Veprs 5.45 and 7.62 have M14x1 LH. it would be safe to assume that .223 has the same one, although i don't own .223 vepr to say for sure.
Even if it's something else it'll be something common and there are plenty of different muzzle devices for most common military thread patterns. maybe you won't find something uber-specific for a QD silencer but there is also plenty thread adapters out there. Hughes Precision sells pretty much any type you'll ever need and they make them on the swiss lathe, so precision is assured.