M1 Gas Cylinder Lock Looseness

[Mauserdon]

I've heard that some will peen the splines on the gas cylinder with good effect.

[togor]

Maury,
That's why I like glue so much.

So, should I peen the splines? Or let the glue take a set before I position the gas cylinder? Or swap around some cylinder locks? The way it is now, the gas cylinder is tight against the handguard ferrule.

Remove the gas cylinder (use wood block against bayonet lug). Clean away old loctite (acetone helps with removal). Reinstall gas cylinder with judicious amount of loctite (I use red myself, withstands heat better). Only this time, FULLY REASSEMBLE the gas system BEFORE the loctite sets up. It will cure with the cylinder by definition in the right place. When it's done you'll find that the cylinder lock bottoms out a little past 6-o-clock, and that there will be a little gap between the gas cylinder rear ring and the front handguard, which is exactly what you want.

[Maury Krupp]

With the gas cylinder tight against the handguard you can expect vertical stringing as the barrel heats up. You need a gap to allow for expansion. The .015in you'd have if you draw the gas cylinder and lock together is probably enough.

Peening the splines is mostly done to:

-Eliminate lateral play of the front sight
-Tighten the fit in the gas port area to prevent leakage
-Help prevent fore and aft movement of the gas cylinder

A hand tight to 5 o'clock gas cylinder lock doesn't make a difference in function; it does seem to make a difference in accuracy. Getting one usually involves going through a big bucket of locks until you find one. If you're building a full-up national match rifle it's worthwhile to get one. If just accurizing a Service Grade maybe not.

Some armorers use Loctite or glue; some don't. The gas cylinder shouldn't need to come off until barrel change so it's up to you. It might help secure everything if the lock doesn't rest on the barrel shoulder; I'm not sure

Glue is a DQ for an "As Issued" rifle' peening isn't.

Maury

[BottleBaby]

Guys, I am here to tell you that green Loctite #294 is A-OK.
Don't worry about it getting hot and coming loose, 'cause it ain't happening this side of a machinegun!

Maury, what you wrote really summed things up for me. Thanks.

[rotorwing70]

Bottlebaby,

It’s my impression you are trying to remove any gap at the front handguard and the rear of the gas cylinder? Bad idea!! First as Maury said, there needs to be some gap to accommodate heat expansion, secondly with the gas cylinder pushed that far back the gas cylinder lock is most likely running out of threads and landing out on the barrel chamfer. If that is the case a boxcar full of locks won't solve the problem.

[MEHavey]

Peen the splines.

Do it gradually and check engagement as you proceed so you needn't worry about over-doing things.

Take a look here to make yourself comfortable:
Garand Knowledgebase - More gas cylinder tightening tips

The biggest tip is don't remove the gas cyclinder when cleaning. Everytime you do, you loosen it up more. Stuff a twisted-up piece of paper towel w/ BreakFree on it into the cylinder to block solvent coming through the gas port when cleaning, then twist it around afterwards to have the BreakFree clean and protect the inside & piston face before pulling it out.

Put the gas plug back in and you're done. (You'll always have maybe 30-45degr of over-rotation of the clinder lock before you rotate back to align with the cylinder. That's normal.)

[BottleBaby]

I glued the gas cylinder back on.

First, I determined where it should go. Next, I screwed on the cylinder lock short 1/4 turn and pushed the gas cylinder up against it. Then I applied the wicking Loctite 294. Once that locked the cylinder in place, I tightened up the cylinder lock the final 1/4 turn.

Everything is tight and secure, the sight does not wobble. There is a 15 to 20 thou clearance between the gas cylinder and the front handguard - just enough for a slight rattle.

Just cracking the screws on a NM AR front sight tower moves the POI 2 minutes; I expect this mod to improve horizontal dispersion by at least 1/4 minute, probably more like 1/2.

[mousegun]

This gas cylinder issue is a little more complex than just making it tight. Most gas locks I've seen won't snug at the necessary five o'clock position so we're stuck with pulling the cylinder up to the lock with the gas lock screw. This puts all the cylinder force on the barrel threads and not the shoulder, accelerating thread wear. This can make gas port alignment problematical, increase the front handguard gap, cause the rear ring on the cylinder to touch the barrel and make the whole assembly sloppy as the threads wear out.

A tight cylinder can be done by:

1. Peening (JCG legal)
2. Shimming (beer can special)
3. Gluing (aka Loctite)

Any of these methods should be accompanied by checking gas port clearance (close to centered in the square cylinder port) and handguard gap (0.125" approx.). Also, use temporary shims to keep the rear cylinder ring from touching the barrel. The rear ring, if jammed against the barrel, can cause parasitic vibrations that will open up groups and possibly loosen the cylinder again. Once the cylinder is secured, pull the shims out.

Milling a new shoulder on the gas lock isn't recommended because it would compromise the hardening of the lock. I've tried using a circular shim, but the angle of the shoulder makes the shim squirm away from the barrel.

Peening is good if done right and can last a long time. It will survive several complete stripdowns and isn't hard to refresh. The problem is that it's a permanent alteration of the barrel geometry. I guess that only counts if one is squeamish.

[gary]

The rubber o ring will work try it maybe $1.00 cost if it doesn't work you can always peen the barrel i just cant see beating on the spline of the barrel
but as i said thats just me i learned a few tricks from a retired Gun Smith in are club best of luck to you

[Devil Dog]

The "O" ring is fine for taking up the slop in the hand guard. Some guys find the loose hand guard annoying. However, I don't see how an "O" will tighten up a loose gas cylinder.