It went something like this -

The "proper" MS with split bridge and all metal construction was made up until about 1972. They then brought out the M72 which was a front locking, 60 degree bolt lift action with a plastic mag rotor and some alloy parts in the mag. Soon after that they started producing the rear locking Steyr Mannlichers with the makrolon trigger guard and removable rotary mag.

Cheers

GG