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I plan on unitizing my gas cylinder/front band. I know there are at least two widely used methods: the Army Method (AMU) screw and glue and the Marine methods (welding). I understand that both of these methods can also be shimmed to tighten up the gas lock at 4-5 o'clock for a nice tight fit at 6.

:?: If gas lock threads are timed, do you still need shims?

:?: :?: Does the AMU method of unitizing lock the spindle valve in the open position due to the screws? Is this a "bad thing" ?


:?: Isn't it advised to close the spindle valve during cleaning to avoid contaminating the gas cylinder? If you have the AMU method you can't do this - so do you clean upside down with muzzle tilt?

Any answers, observations or comments?
 

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If gas lock threads are timed, do you still need shims?
If it lock up tight at 6 o'clock then don't use a shim.

Does the AMU method of unitizing lock the spindle valve in the open position due to the screws? Is this a "bad thing" ?
Yes it does lock it open. But why is it a bad thing. How often do you shoot grenades so need the gas shut off??

Isn't it advised to close the spindle valve during cleaning to avoid contaminating the gas cylinder? If you have the AMU method you can't do this - so do you clean upside down with muzzle tilt?
Field stripping for cleaning the gas cylinder plug & gas cylinder are removed so everything gets cleaned.

HH
 

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I clean mine upside down with the muzzle down--keeps solvents out of the gas system (which I clean every 300-500 rounds) and also out of the bedding area of the stock.

If you have access to several gas cylinder locks, you can just try a bunch till one of them stops where you want it to. Otherwise you can use shims. Or you could just live with it and probably be just fine as long as the gas cyl is TIGHT on the barrel splines.

Ty
 

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Hueygunner, a member of this forum does the work for a nominal fee, and does an outstanding job. He uses the screw method, reparks the front band afterwards and ships it vacuum packed back. Quick turn-around too.

Check the Slop Chute for some feedback on his work.

Regulator
 

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Not to step on anyones toes, but Gus Fisher answered this question over on Culver's. He recommended the weld method over screw & glue. He said that shooting team members who shot 200 to 300 rounds a day were shaking the screws loose. He did however say that the average civilian shooter would probably not shake a screw & glue loose.

Regards

Ox
 

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Oxmix said:
Not to step on anyones toes, but Gus Fisher answered this question over on Culver's. He recommended the weld method over screw & glue. He said that shooting team members who shot 200 to 300 rounds a day were shaking the screws loose. He did however say that the average civilian shooter would probably not shake a screw & glue loose.

Regards

Ox
On my gas cylinder, the screws have been staked, so I do not believe the screws coming loose will be possible. Not everyone stakes them, but hueygunner does.

I have read some negative comments on the welding method due to the possiblity of distortion or slight warping of the gas cylinder. Also I have to believe after welding the appearance would be changed as you could not repark the front band, and the welding would definitly burn off the black oxide coating on the gas cylinder. The only way to refinish is painting, and while that would make it black, it wouldn't look original any longer.

Like you say, the average shooter would probably never shake a screw loose, and with them staked, it is even more unlikely, so that is the way I went, screwed and glued.

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Judging by the amount attention this NM mod gets, I presume it is truly worth-while. I shimmed my gas cyl so GS lock tightens properly, doing this really locked in the fit of the stock/hanguard/frontband. Can someone explain WHY unitizing the gas cyl to the frontband is so worthwhile?

thanks,
Dave
 

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woodpuppy said:
Can someone explain WHY unitizing the gas cyl to the frontband is so worthwhile?

thanks,
Dave
I think it is basically so at the range we can act cool and say "yup, had the gas cylinder unitized", while we can't begin to shoot well enough to appreciate the differance. :lol:

Just kidding, sort of. Others can explain the advantages technically better than me.

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woodpuppy said:
Can someone explain WHY unitizing the gas cyl to the frontband is so worthwhile?

thanks,
Dave
I'll give it a shot.

When the gas cylinder and front band are unitized, they become ( by definition) 1 piece. This method offers repeat allignment of the stock ferrule and front band which increases accuracy.

When they're used seperatly in 2 parts, they'll move, twist and turn against each other. This will cause a shift on the stock ferrule and front band and may not always line up in the same place after each shot.

Hope that I explained it well enough.





 

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thanks Warbird, that makes sense- especially when you think of the rifle bucking under recoil, with sling tension as well. So to sum up, it helps to minimize shifting about of as many parts as possible so parts are aligned the same shot-to-shot.
 

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Re: shim and unitize ?

M14rick said:
just my thought- if a unitized gas cylinder were shimmed, there would be very little or no vibration to cause loosening of the unit...any feedback on this?
Even though it may not be moving, it's still getting fatigued with each squeze of the trigger.

The obvious benefit of a unitized gas system is that it locks up the barrel band which would normally rattle on the barrel. Also, it's not going to shift around like it might on a regular gas system that's been shimmed tightly.

Ty
 

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Hey, just thought of something else-

If your gas cyl & front band have been unitized, should you use shims, or should you NOT use shims? If the splines locate the gas cyl around the axis of the barrel, and the gas cyl lock locates the gas cyl with respect to the gas port in the barrel, is there ANY reason to add tension to the barrel by shimming?
 

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To shim or not to shim? I'll try to answer this -

It depends on where the gas cylinder lock ends up when tightening it to install the gas cylinder. If the lock doesn't start to get tight around 4 o'clock and require some 'tapping' with a mallet to seat at the six o'clock position, you should shim the gas cylinder to acheive this. This will insure that the gas cylinder is not free to move on the barrel splines. Doesn't matter if it's unitized.

On most of the un-shimmed installations that I've seen the lock will travel past the 6 o'clock position to around 8 o'clock and will have to be turned back to align at the 6 o'clock position, regardless of whether the cylinder is unitized or not. Theoretically, this is too loose and might allow the gas cylinder to move.
 

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Screw and glue method

When I was trained to build NM M-14s in the military by NGMTU we were taught the "screw and glue" method of unitizing. This can be a complex procedure. The front band and spindle valve were first annealed in an oven. Then the gas cylinder components are locked together in a special fixture and drilled/tapped/countersunk for screws. Screws were glued and staked. When the unitized assembly was installed on the barrel there were no shims used. We tightened the splines and positioned the gas cylinder relative to the gas port. On G.I. NM barrels there was usually a slight gap (maybe .005") between the gas system and barrel shoulder. The theory was that a tiny gap was needed for heat expansion without inducing stress. I have unitized M-14 gas systems for years with this method and never seen one shoot the screws loose. The USMC welded theirs.
 

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Sherlock308 said:
To shim or not to shim? I'll try to answer this -


you should shim the gas cylinder. This will insure that the gas cylinder is not free to move on the barrel splines. Doesn't matter if it's unitized.
Actually, if the gas cylinder plug is torqued correctly, that's never a problem.




Sherlock308 said:
On most of the un-shimmed installations that I've seen the lock will travel past the 6 o'clock position to around 8 o'clock and will have to be turned back to align at the 6 o'clock position, regardless of whether the cylinder is unitized or not. Theoretically, this is too loose and might allow the gas cylinder to move.
Again, not a problem if the gas cylinder is properly torqued.

It's been reccomended that a gap of .003 minimum between the gas cylinder and barrel shoulder be maintained for a barrel to expand and contract.
Putting stress on the barrel at the shoulder would and could defeat the purpose of unitizing.




 
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