The distance from the striking surface of the bolt carrier to the face of the installed piston is critical. The AKM and AK74 bolt carriers make firm contact on the left-hand side when in battery. The Type 3 AK and all AK-type arms made by Zastava make firm contact on the right-hand side when in battery.
The link below opens a file that shows the relationship between the datum point of the bolt carrier to the piston face for the Type 3 AK, the AKM, the AK74, and the AKS74U.