I had an idea for a yugo sks ( the model 59/66 )the one with the gas shut off for launching rifle grenades.With the gas port closed you would have no chance of gas leaking around the piston if you were using a supressor,the action would not cycle so that would cut down on noise as well.Added benifits are that low pressure subsonic loads could be used (hand cycled) just like a straight pull steyr 95,brass would not be thrown about.andyou could switch back to standard ammo and semiauto in less than a couple of seconds.  Just an idea though.