SA Gas Cylinder

gnmontey

gnmontey

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I purchased a Springfield Gas Cylinder from Brownells in order to make use of my $40 adjustable gas plug (money pit). It can get the cylinder to seat on my norc barrel, but only with a LOT of persuasion. It's very very tight. Kind of makes shimming a joke as there is no way one will move the cylinder position by screwing down the cylinder lock.

In comparison, I can knock off my norc cylinder with a rubber mallet. The SA I have to use a BFH and wood blocks.

Is this to be expected?
 
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use a black felt pen on the contact surfaces of your barrel
then try and fit the assembly, as far as it will go with hand pressure and see where the wear spots are.
my guess is you will need to use emery cloth on the barrel contact points to bring into spec.
I had to do this on my krieger barrel to get the oprod guide AND a usgi gas aseembly to fit up. Incidentally I prefer to have mine tight enough that a BRM (big rubber mallet) is required.

Be sure to clean out the barrel gas port .

and this is an important thing to note as well.
If the fit is so tight it is distorting metal..... watch for metal flakes ar metal movement arounf that barrel gas port.... you don't want that.
 
Possibly, ACP has the right answer I usually peen the Splines to increase friction to ensure it fits snugly, tight is OK it will come off OK after a few times remember not to swing the hammer to hard
 
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I'd have to do the same to put my smith enterprise gas cylinder on a norinco barrel. The splines seem a thousand-of-an-inch or two taller, I can't get an accurate measure though.
 
You may also want to check the OD of the barrel where the gas cylinder slides on. The spec is 0.680 +/- 0.001 inches. If the barrel is more than a couple thousandths bigger it would be hard to get on. I am running into this because my gas cylinder swelled a bit when we welded it. The ID of my USGI gas cylinder is now 0.676 and it won't go on. Doesn't take much when you are talking about fine tolerances.
 
powmia56 said:
You may also want to check the OD of the barrel where the gas cylinder slides on. The spec is 0.680 +/- 0.001 inches. If the barrel is more than a couple thousandths bigger it would be hard to get on. I am running into this because my gas cylinder swelled a bit when we welded it. The ID of my USGI gas cylinder is now 0.676 and it won't go on. Doesn't take much when you are talking about fine tolerances.
Click to expand...

How did you resolve this problem?
 
45's suggestion pointed out the bind points. A little work with emery cloth on the inside of the gas port cylinder ring solved the problem. The machining on the gas port barrel band is pretty crude. I didn't want to muck with the barrel in case I have to return to using my norc cylinder.

Something of interest surfaced with this project. Upon close inspection of my unitized norc gas cylinder it was quite evident that two of the tack welds had come close to penetrating the barrel. It may have been just plain luck that the cylinder hadn't been permanently tacked to the barrel.

And on another note: The norc cylinder/piston is a step ahead of the SA unit. The SA cylinder/piston fit is quite sloppy in comparison to the norc.
 
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mikebaker1129 said:
Did you purchase a new piston as well with the SA unit or did you use your NORC piston in the SA gas cylinder ?
Click to expand...

45 gave me a heads up that there was a slight dimentional difference between the norc and SA piston (the norc cylinder/piston are apparently chrome plated) so I purchased both the cylinder and piston from Brownells. If you are going that route don't forget to order the spidle valve and spring at the same time (I didn't, and ended up issuing a second order). Save some money on shipping.

Also of interest is that I got dinged $10 by customs for "handling" for an order that was approx the same value as my Boyds stock from DM which wasn't charged? Don't know how that works.
 
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once proper fit has been achieved by establishing and adjusting contact points .... you can then peen the barrel splines to establish correct rotational alignment or to remove rotational play, if any is present.
then with gas port aligmnent being observed throughout the procedure.... decide whether to shimm or peen the barrel shoulder, at the gas band to acheive desired lock up of the gas lock and to remove latteral play in the gas assembly.

a note on shimming.
for a fun gun where rapid fire and a hot barrel are likely to be the role of the firearm...... your gas lock should come tight at about 7:00 to 8:00 and then be backed off to 6:00. Running the assembly too tight on a hot gun can lead to problems down the road and can lead to vertical stringing on the range. For these rifles i like to tig weld the front band to the assembly and run without shims if possible.

A rifle intended to be a match gun or a hunting rifle where accuracy and slow fire are the normal role for the rifle..... we want the gas lock ring to come hand tight at 4:00 and tool tight at 6:00

all the while observing gas port alignment with the back end of a 1/32 drill bit or similar drill rod.
 
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