I have been shooting my M1A regularly at the range and at matches for the last ten years. I have several rifle team budies in the same boat. I have fired thousands of rounds of commercial rounds as well as my own reloads with commercial primers. I have never had, witnessed or even herd claims of a "slam fire". I think that this has become an issue because it is "mechanically" plausible and the word "liability" popped up in some board meeting.
I regularly drag out “the stick” and shoot it, and shoot a Garand in competition a couple of times per year. I am on the third match barrel of one of my M1a’s. Shot it last weekend in a reduced match.
Early on in my shooting career I had a severe slamfire in 30-06 with a garand. This was in the middle 80’s and I was firing the round sitting rapid fire, and the round was the last round from the eight round clip. The bolt had partial engagement. I lost the elevation knob, split the stock, and I would have had brass particles in my eye if my glasses had not protected me. The round was a reload, the gunsmith told me my rounds were not sized enough, and the primer was Federal.
That was when I learned from Gene Barnett, the barrel maker, that ammunition had to be sized smaller than the chamber. I purchased from him reamer cut cartridge headspace gages and used them. Along with Wilson cartridge headspace gages.
While I always feed from the chamber, I had another 30-06 slamfire with Federal primed ammunition in the standing slowfire phase. The round was fed from the SLED, the round went over the birm. Because the lugs were engaged nothing happened. I figured it was something I did.
My last slamfire in 30-06 was with brass sized in a Bonanza match die. This brass was once fired LC 60’s vintage match. I reamed all the pockets to depth and had primed them with Federal primers. When I gaged the loaded cases, the cartridges were only a little long: only an amount equal to the rim thickness would not fully go into the Barnett gage. So I thought I was safe, after all the conventional wisdom was that only “high primers” caused slamfires. In a new match Garand, firing from an eight round clip, one of these rounds slamfired out of battery and blew the back end off my receiver. My glasses were shattered and the blown out heel of the receiver cut my eye socket.
That is when I learned, absolutely, positively, that conventional wisdom is 100% bunk.
The Garand firing pin is almost a half inch longer than the M1a firing pin. Being heavier it is more likely to slamfire than a M1a mechanism.
I have talked a lot about this with fellow shooters. A surprising number who would not have broached the subject unless I mentioned slamfires. People do not like to volunteer information on accidents they have had. However, I met with three shooters who experienced catastrophic slamfires. Two of these were with Garands and one with with a M1a.
The M1a shooter was imitating a slow fire technic he had seen at Camp Perry. Some competitors were slightly unlatching their magazines during the long range phase, placing a round in the chamber, and dropping the bolt on the cartridge in the chamber. His rifle slamfired and his receiver had to be replaced. He was using Federal primers. He stated that he got more careful about how he reloaded ammunition after that.
One gentleman had a Garand rebarreled to a match 308. His rifle slamfired out of battery with Federal primers.
Within the last couple of years, a shooter I know had a Wilson match barrel installed on a Garand receiver. He wanted a Garand Match legal rifle. He was given a standard sizing die, used that, and used Federal primers. His rifle slamfired out of battery and blew the back off his receiver. His comment to me was “people ought to know how dangerous those rifles are to reload for.”
I have been on the line at Camp Perry, during the Garand match, when the CMP issued, Federal made ammunition, slamfired in somone’s rifle. A nearby bud told me more. It was during the Slow Fire standing stage, on the load command. The unfortunate had his safety on, placed a round in the chamber, dropped the bolt, and the rifle slamfired in battery. I heard it, everyone heard it.
I guess you were not there.
Just because you have not experienced or seen something, and your friends have not seen or experienced something, does not mean it does not happen.
You really have to be more careful reloading with Garands and M1a’s than any other rifle out there.
You can find proper reloading advice all over this forum, if you look.