Its just a thought,but did ya think about polishing the chamber? You might only have a rough chamber, plus it can't hurt. I have heard of only a handful .308 conversations working correctly. Most problems were traced to the gas system (as I recall) and ocassionally the extractor.
I had a 49/56 in 7.5 French. The ONLY gripe I had was problems finding ammo and the price of same. Also the original ammo is corrosive.
The MAS I had looked almost new and was very accurate. There was a guy located in Arkansas who used to modify FAL mags to fit the MAS 49/56. These FAL mags held 25 rounds of 7.5 French. He used to advertise in Shotgun News.
Herb has a good idea. If ya don't want to work on getting the bugs out buy one in the original caliber and make up your own ammo. RCBS was making dies to convert Swede brass. If I had a place to reload I would have kept mine . It is a very reliable weapon. If ya run out of ammo it can double as a club or paddle!! LOL
BTW,before you polish your chamber check it out good. I can't recall if the MAS had a chrome bore & chamber,but I doubt it. Better safe than sorry.