OK, I NEVER use gas shims on any of my M-14, because adding the shims involves you in :
A: Cutting the shims into a "C" rather than an "O", SO YOU CAN SLIP THEM ON WITHOUT REMOVING THE FLASHIDER [ welded on in most cases ].
OR,
B: removing the flashider ... which on some of these is definitely NOT trivial
{I prefer the Chopsaw method of removal ... and I then end up with a "SHORTY"}
OR,
C: using a machinest's self striking center punch to stipple metal at the REAR of the gas assembly / front of the barrel shoulder. I also peen the grooves of barrel, to remove all radial play. Just make sure you use a small drill bit to ensure the gas hole in the barrel [ SMALL hole] still lines up inside the hole in the gas assembly [ BIG hole ], otherwise the gas takeoff can be constriceted, and .... YOUR #### MIGHT FALL OFF!!
PS: before you get all bent out of shape over gas assembly shims ...
the majority of the NEW 14s we have seen recently had the gas lock / "8" ring installed BACKWARDS.
Simply reversing the gas lock tightened up many of these rfiles with no other parts or effort needed.
BUT of course, reversing the gas lock brings you back to number B: ... removing that darned flashider.
SO,
what other firearm out there gives you so much bang for the buck ... AND, and excuse to buy a new chopsaw??
[;{)
LAZ 1