I have the 7.62 NATO conversion from Century
the particular one I have shoots fine, I'd found information on Surpluserifle Fourms and Gunboards Fourms that address the issue.
if your shooting commercial soft primers they recomend tipping the firing pin slightly to slightly remove the radius of the pin (blunting it)
another has a firing pin return spring, and another they make one of Titanium,
I opted for tipping trhe firing pin as per the demensions outlined in the SurpRifle Fourm and did manage to get a small enugh return spring fitted to my firing pin (requires turning a step on the hardened firing pin),
If your reloading, you can simply purchase the Military primers and do away with all the above mentioned foolishness.
The Mas 44, 49, 49-56 were designed to fire military ammunitions also used in machine guns, such ammo had a thick primer cup that needed a good whack.
If properly adjusted, the firing system of the Mas 49 and 49-56 with its free floating firing pin should not slam fire on hard primers.
the correct protrusion of the firing pin inside the bolt face is
Many Mas 49 and 49-56 sold on the French domestic market have been transformed to fire "civilian" calibers like the 30/284 by rechambering or 7.08 by rebarrelling, the gunsmiths have also adapted the firing pins for commercial ammo by blunting the firing pins with a flat end reducing the protrusion from 1.3mm down to 0.8mm.
The gunsmiths have also checked that the trigger block is properly adjusted inside the stock:
The correct protrusion of the hammer inside the receiver must be adjusted very precisely:
The measurement is checked with the trigger depressed and the hammer is held back by the auto sear.
The poor adjustment of the trigger block is the most frequent cause of burst firing by the Mas semia auto rifles.
What happens is not a real slam fire, as the bolt is already locked when the firing pin is allowed to move forward and touch the primer cup.
For reloading ammo for these rifles CCI 34 primers are a must.