M14 Forum

tonyben

I've setled for a gas cylinder that was really tight on my barrel for a couple of years now. I can get good 1.5" groups out of it but it has always bothered me that the gas cylinder was so tight that I had to hammer it on. I can never get the groups under 1.5".

This weekend I finally got the cylinder off and I used some jewelers files and opened up the inside loop that has the splines. It took about an hour of filing and fitting.

I shined a LED flashlight behind the loop and looked for light seeping through the gaps. I was able to file the high spots to get the cylinder on farther. The lower section under the barrel was the part that needed the most relieving. That area and the top of the side splines were binding. It bound the same on 2 barrels; a GI H&R barrel and a Criterion Medium weight.

Once I could slide it on about 2/3rds of the way on without resistance, I mixed up some lapping compound and worked it back and forth, tapping it into place and then using a small screwdriver to pry it forward. After lapping a couple of times it now fits to the point where I can slide it on by hand until it's aligned. I added some shims and got the gas lock to snug down at the 5:00 position. It takes hard finger force, but now I can fully time the lock at 6.

My question is that if the cylinder fit too tight on the barrel can it degrade accuracy?

I will be trying this out at the range this weekend (hopefully). I am hopeful that relieving the stress will help me break that 1.5" barrier and get below 1". If not, It's time to reglass it, this time with Marine Tex.

Thanks

Gus Fisher

Yes, especially if it sets up real tension between the barrel and both rings of the cylinder. Now, that doesn't mean it can't be tight on the barrel, but it should not be tight as to cause "twisting" tension forces on the barrel. Not sure if I have explained that very well.

tonyben

Thanks Gus. Looks like I can try it out on Saturday.

I should add that the rear ring around the gas port provides no binding when it slides on. The tension was all in the front ring with the splines. With the clearing I did, and adding some grease, it slid on and off with moderate hand force. Not too tight, not at all loose. I had been wondering if the tightness I had before was causing a "tight spot" in the barrel when the bullet passed through that point.

Tony.

art luppino

Hello Tony,

The best way I have found is to remove material from the barrel to the point the ring slips over with light hand pressure. Peen the splines and add epoxy to the area, tap cyl on than repeat the process a second time. Clean up and see if the groups tighten up.. Art

tonyben

So you essentially mate the cylinder to the barrel for life? Although I do know you can use heat to remove it, but I take it you intend on it being a permanent mouning solution; correct?

MemphisMachinists

Tony. You may not have realised it. but you opened something of a can of worms. So If the gas cylinder needs to be an easy slip fit; what about the op rod guide. I have been going to a lot of trouble fitting these buggers after a PM from a certain Kerrville. Texas
14 smith advising me about how they should fit. Anything hanging on the barrel is gonna affect how it shoots.
Personally I am willing to accept the negative efffets of the gas system so that I don't have to cock the damn thing. Call me lazy.

Gus Fisher

I don't want to speak for Art, but what he is talking about is a GC slip fit on a NM rifle AND epoxying it in place so it is tight afterwards. IOW, the metal to metal fit has almost no stress involved and the epoxy holds it tight.