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3,167 Posts
Hey there - HH. It's good to see you finally have some time to thnk about something else other than surviving the hurricanes.

I hope this is what you are referring to. FWIW - the shimming should be done between the front band and the shoulder of the barrel. By placing the correct thickness of shims in place, your gas cylinder lock will tighten up around 3-4 o'clock and snug down correctly at 6 o'clock.

I did this some time ago and here are several old posts that describe the process. It's best if you have either the Duff or Kuhnhausen books because they both have good instructions on how to get the job done right.

Here goes - hope this helps a little - just make sure you don't make the same mistakes I did. It turned out OK, but it was a lot more work.

Hawk said:
The shims go between the front band and the barrel shoulder. This is for allignment for the gas port only. The gas port must be alligned properly for proper functioning of the gas system. I looked it up in Scott Duff's book to see what he says about it (pg 144) After installing the gas assembly and front band, tighten the gas cylinder lock on the gas cylinder. The lock will probably stop past the 6 o'clock position. After tightening the lock, back it off to 3 o'clock, check with feeler guages to see what shim thickness is needed when you snug it back up with the feeler guage still inserted to the 4 o'clock position. He also goes on to say not to back up the cylinder lock more than a whole turn as it will throw off the allignment with the gas port. The lock should be snug at 4 o'clock so when turned to 6 o'clock, it securely clamps the loose front band. Hope this helps.
Post to Spartacus... if there is any "wiggle" room between the gas cylinder and the front band, then you are a prime candidate for some tightening up by shimming the gas cylinder.

Both Duff and Kuhnhausen state in their books on match conditioning, that the looseness I just mentioned is one of the prime factors in lost accuracy potential of your m14/m1a.

My gas cylinder was so tight on my m1a that I had to take a wooden block and a plastic/rubber headed mallet and drive it off so I could do the shimming job.

As I stated in a previous post, the flash suppressor and gas cylinder loosened up a bit in the removal and replacement, so I got out my old trusty 1/8" punch and my small ball peen hammer and peened the edges of the the splines a little to tighten things back up. It's not really hard to do and it's not hard to judge when you've peened the splines enough. The gas cylinder will not press on by hand and you'll have to use the block and hammer to lightly tap things back into place - nice and tight.

I understand your reluctance because I felt the same way. Thank God for the guys on the Firing Line. Because of their good advice and encouragement I not only increased the accuracy of my rifle, but I learned some cool new stuff, too.

I did the job myself and if I can do it, you can do it.

Let us all know how things go - this is one mod that will help you keep all the holes in or around the little bitty "X" in the middle.

Have a good one,

p.s. If you don't want to take things off your barrel, you might want to get some info and advice from our very own "Warbird". A while back,Tim posted some info about cutting the shims so you don't have to remove anything.
Since I started this whole thing, I guess I should report on my finished work.

The final installation worked just fine. I got the gas cylilnder realigned properly and got the shims installed with a minimum of problems. Everything is nice and tight. Can run a drill bit all the way through the gas cylinder into the barrel with no problems.

Looking down through the hole in the spindle valve, I can see that the gas hole in the barrel is slightly off of dead center with the gas cylinder, but I don't think that should cause any problems since it is a very slight offset.

I must admit, that I wish I had known about cutting the shims and not having removing the gas cylinder or the flash suppressor. I wonder why Fulton Armory or the other suppliers don't make them that way? Sure would be a lot easier than what I went through.

Had to take an 1/8" punch and a small ball peen hammer and peen the splines on both the gas cylinder and flash suppressor to tighten them back up. Just tapping them off and putting them back on loosen things up considerably.

Thank God I had both my Duff and Kuhnhausen books. Together they cover just about everything you need to know.

The moral of the story is this: get all the info you can, the right parts and tools and just do it!!! If I can do something like this, anyone can. (even enjoyed it).


434 Posts
They're little stainless steel rings that just fit over the barrel. Fulton Armory has them
HERE for $7.95 a set. The set I ordered (a while back) had 3 shims. Worked great.

79 Posts
After reading about how to tighten the gas cylinder/front band fit using shims, I remembered I got some with the gas system rebuild kit from Fulton- I ran home and whipped out some feeler gauges, added the .016 & .010 shims, and she's rock solid!! Barrel gas port is dead-center in gas cyl port. Topped it of with a NM flash hider with bayo lug, TA DA! Now I've got to go get 'er zeroed this weekend.

great instructions.

er, after finding different's site, it appears I got hosed and have a repro FS. D'oh! still better than the naked FS I replaced.

8 Posts
I was wondering if there is anything special involved in cutting the gas cylinder shims for installation without FS removal. I tried the search function for references to cutting the shims but drew a blank. My SAK barreled GI Collector model M1A definitely has wiggle in the front band. I have the shims from fulton. I would rather not remove the flash suppressor if I don't have to. Any help appreciated.

3,167 Posts
Hey Guys - I pm'ed Warbird for some good advice on how to cut the shims and this is the reply.

From: warbird
To: duckbuck
Posted: Sat Sep 18, 2004 12:22 am
Subject: Re: Cutting Gas Cylinder Shims
duckbuck wrote:
Hey There Tim - a while ago you posted a method for cutting gas cylinder shims to avoid taking off the FS and gas cylinder. I've looked all over and can't find the post.

Can you give us a hand?

Here is the tread. http://www.m-14forum.com/viewtopic.php?t=8185

Hunting Hawk started the tread and several others wanted info.

If I can find all the info about how to do the install, I'll post a thread in the Intel Section. Of course, the first thing on the list will be to buy the Duff/Kuhnhausen books.

Thank you, Sir.


Howdy Dennis,

You can use tin snips or heavy duty scissors to cut them.

Then remove the gas cylinder plug.
Then remove the gas cylinder lock.
Move the gas cylinder forward and install shims needed to properly space the gas cylinder.
You may have to try different shim thicknesses to get the correct lock up of the gas cylinder lock at 5:00.
Then install the lock and plug.

Regards, Warbird

Warbird's Custom Guns
Warbird is a real pro at this stuff and I appreciate him helping out here.

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