GC locks

[milboltnut]

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[RCS]

sometimes changing the front hand guard will allow you to find the right timing

[milboltnut]

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[togor]

sometimes changing the front hand guard will allow you to find the right timing

Handguard shouldn't bind on the gas cylinder in any case, so not seeing the linkage there. On regular non match shooters a bit of loctite on the GC splines gives the same outcome as a perfectly timed lock. Full strength loctite can be a bear at disassembly but medium strength comes apart fine with some acetone.

[lyman]

old man taught me a trick to tighten up, and time GC locks,


put the barrel on a sturdy surface, (or clamp in a vice)

take a large flat punch, or if you don't have one big (wide) enough, use a ball peen hammer,

put the flat section on the spline, be sure you are contacting both sides of the spline, (the punch or hammer is basically straddling the spline cut, you can do all 3 if it makes you feel better, )

tap with a hammer (as in tap the punch or hammer)

not too hard, and it make take a tap or 3,

you are basically constricting the spline cut to help tighten it up,

MUST be sure to get both sides evenly, and not hit to hard,

[togor]

For some reason every CMP rifle I have received, even the very low miles ones, had a loose GC. Makes me wonder how many times the cylinder is getting pulled in military service.

[lyman]

not sure of the cleaning regime, but they are not built to be tight, just work,

match shooters want them tight, the .gov and . mil just wanted them to work

[togor]

Right but in my parts stash I have two NOS cylinders that when they go on the first time, it will be with a mallet. So the front ring stretches with each replacement cycle, such that by the time I get them from the CMP, even circa '07 correct grades that are hardly used, the cylinder is loose. Peening is the SOP but for pampered living loctite has the advantage of not pushing metal around, which is an irreversible process. I have 3 I shoot regularly and the others hardly at all, plus one grade B receiver waiting for my son to say "when". At his age there are more interesting things in this world than rifles.

[lyman]

I've put together rifles with new cylinders, and used (or lightly used if you go by the finish) cylinders, (that all gauged perfect too)
some tight, some, not so much,


think about it this way too,

brand new gun issues to a unit,
it gets Gauged once a year, or so, and if shot for quals, then cleaned at least once , or more,

each time it is cleaned, it is taken off,
each time a gauge goes on a firearm, it is taken down (gauge the gas cyl wear, and the barrel wear at the gas port)

so that new correct gun may have been apart 25 times?, 50 times? who knows,

or it may have been skipped over as it set back in a rack in an armory that just got new M14's or M16's and they did not get sent back for years,


again, who knows,

[Orlando]

not sure of the cleaning regime, but they are not built to be tight, just work,

match shooters want them tight, the .gov and . mil just wanted them to work

When originally manufactured they were very tight, the cylinders were actually pressed on.