BTW, I've noticed the Russain Saiga AK guns have the piston screwed down TIGHT in the carrier! 
Kalashnikov would roll over in his grave, I'm sure.
Seriously, I think AK's were made with a "loose tolerance" especially in the action so I would think that the piston would have to have some slop to compensate for movement in the action.
We in the USA have an obsession with tight tolerances like it's the only way that there is to design, but creativity and genius seem to rise to the top every time. IMO.
Thanks Lolly!
Billy