Thank you sir!! Great adviceJust my 2 cents...
Being a tinkerer playing around with what other guys have shown me about the M1A/M14 platform, i did become a fanboy for shims and unitizing the gas cylinder. Did not arrive there easily because i just could not wrap my head around changing something that appeared designed into it. However, the thought of the gas lock rattling on the barrel threads just never set right. I mean why bother having a barrel shoulder if not gonna use it?
Over the years, some of my M14s shot straight and true while others that looked and fit the same would string shots and/or make two groups about 3 inches apart which, to me, indicated something moving between shots. Yeah, for defense, 2 1/2 to 3 inch groups at 100 is awesome but i wanted more. Like, shooting old apples across the pasture at 300. The shims and unitized cylinder did help reduce the minute movement or changes in harmonics or whatever black cloud hoodoo happens before the rifle settles for the next shot.
Like someone brought up earlier in the conversation, if you over tighten the gas lock onto too much shim pack, weird things happen as the barrel heats up. The same thing happens with no shim and somebody cranks the lock tool hard to line up a 3-4 o'clock gas lock to insert the plug. Same thing.
The biggest advantage to the whole shim thing, imo, is the ability to increase the dwell time to it's max. Yeah, another rabbit hole conversation BUT, my experience on my own rifles running through thousands of rounds shows it makes a diffrence. Be it small or big depends on your perspective.
Shoot straight and enjoy the journey!