I just have to chime in here.
As some of you may know, it all started when I decided to replace the Norky bolt (on my M305) with a 7.62 firearms bolt. From what I read and physically measured (from the copies of the original blueprints), the 7.62 was USGI spec dimensionally. Well to make a story short, I blew the rollers off the new bolt....twice.
After the first time, I thought the bolt was a little tighter, better yet, more resistance was needed to move the op-rod and new bolt to the rear of it's cycle in the receiver (without op rod spring, but with trigger group in rifle), using a very simple system of weights to move the rod, then the Norky bolt.
Hmmmm...that got me thinking. the only reason for that is that something was different. Careful measurement of the new bolt revealed that it was slightly dimensionally larger. I carefully used a little lapping compound and eased some of the resistance. This had the effect of "polishing up the trigger hammer and the underside of the bolt. The receiver was pretty good dimensionally.
I blew the second roller. Hmmmm...something still not right. Plan B...get USGI oprod, spring ad new rollers. I am getting good at replacing those!
Had to do a little fitting work, but installed oprod and does very well with the tilt test. The original question about the M305 vs the M1A? I don't know about the M1A, but I do know for a fact that the bolt and oprod on my m305 were dimensionally VERY different than the USGI equivalent parts. THe oprod was really telling. I think I know what happened to my roller.
The roller us USGI spec, the oprod was not. The new bolt would not glide into battery once the top of the bolt touched the receiver. The oprod was cut such that it actually cradled the roller to almost "hold" it in place. In a few posts back, I noted that shiny "peened" spot on the oprod. This would have resulted in the energy of the spring being borne on the roller once the bolt came to rest against the receiver.
The new oprod also had a very miner hold. as well, I do have tighter tolerances. I very, very carefully ground down a little part of the "hump" to allow the roller to easily rotate down into battery without stopping suddenly. The energy of the spring now is exerted onto the roller indirectly to redirect it so it moves the bolt into battery. The Norky oprod was grossly cut differently, but with a dimensionally inferior (different) M305 bolt, it functioned fine.
I have it lubed up and ready to shoot tomorrow. Lets hope I do not need to replace any more rollers.
Claven and M14 Doctor - thank you so much for you ideas, experience and input.
