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Hi!

I've noticed that there is some gas leak between the barrel and gas cylinder. I've tried with two different GI cylinders and the result is pretty much same. Both cylinders slides easily to barrel and I added couple shims to get correct timing for cylinder lock. The barrel is stainless MW criterion. Can this gas leak effect to barrel harmonics? And how it can be fixed? Thanks!

-Olavirta

430422
 

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As I recall, the SEI cylinders I have used were a tighter fit than USGI.

Make sure your cylinder is all the way on. Tap it against the barrel shoulder and turn the lock until it stops, usually around 10 o'clock. Back it off to 6 o'clock and tap the cylinder forward so that it is hard against the lock. Install the piston and tighten the plug to 15 ft lbs. You should see one full thread exposed on the barrel, in front of the lock.
 

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Using shims is not always a good thing. As the rifle is now with the shims, remove the gas piston. Re-install the gas plug. Take a small allen wrench or nail and send it up thru the hole in the bottom of the gas cylinder. It should pass thru and into the barrel without hitting anything. If you feel it hitting or catching an edge, then do what Kurt recommended. Remove the shims and start from scratch. There is an actual gas cylinder alignment tool made for just such a check.
 

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I had a similar problem with a gas leak, obvious soot from around the gas cylinder.

The gas leak did not appear until after I shimmed the gas lock.

Found a post on this site about placing a shim between the barrel and gas cylinder on the OPPOSITE side away from the gas port, or the top side of the barrel.

Solved the gas leak with a very thin brass shim.

I don't recall the thickness but it was next to nothing.

A little later I installed a unitized gas system (screwed and glued) and did away with the gas lock shims and the shim on the top of the barrel.

No more gas leak.

I'll see if I can locate the post.

Found it.


Read down to Tonyben's posts, it contains pictures!

Tony is a moderator here and a M1A guru.

Search is your friend.
 
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