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Trouble shooting help

1524 Views 18 Replies 9 Participants Last post by  tmcfalls
My rifle shot fine for the first 500-600 rounds, then I found that the gas plug had shot loose, and evidently allowed my piston to cause a small burr on the surface of the receiver side opening. I stoned the burr down and reassembled the rifle, and shot it several more trips. Latter on I completely disassembled the rifle for cleaning and to check to see if the problem was solved. Everything looked fine and I reassembled the rifle after cleaning. The next trip out the rifle would not cycle after the first shot, I can manually strip another round from the magazine and it will fire each time but not open the bolt.

My gas cylinder is unitized, the piston will move back and forth with gravity, and my op rod doesn't seem to be binding on anything with or without the op rod spring attached.

The only thing I have changed is that I have switched to LC brass with a slightly decreased load of IMR 4064 from what I had been successfully using in commercial Winchester brass. The cases did seem to have more soot on them than normal but I didn't really notice anything unusual that would lead me to believe it was ammo related. If I get home in time to day I am going to reassemble my rifle and try some factory Q3130 through it.

My only other thought is that my gas cylinder and barrel are out of alignment. I thought I would check here and see if any of my more experienced M14 brethren had any other ideas for me to try out.
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I think, piston's hole not aligned with gas port, maybe the dirt in the chamber could be enough thick to keep it a little better aligned, and now after cleaning the holes are not matching each other. Or they could be not still aligned before, but the small portion of free space available could be enough to allow the gas enter in the piston's chamber and make the rifle work. Now, with reduced amount of charge, this small portion of gas could not be enough as before.

Just my thinks, hope you can solve!
 

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Discussion Starter · #3 ·
I think, piston's hole not aligned with gas port, maybe the dirt in the chamber could be enough thick to keep it a little better aligned, and now after cleaning the holes are not matching each other. Or they could be not still aligned before, but the small portion of free space available could be enough to allow the gas enter in the piston's chamber and make the rifle work. Now, with reduced amount of charge, this small portion of gas could not be enough as before.

Just my thinks, hope you can solve!
Just for clarification purposes my loads have only been reduced enough to compensate for using military brass.
 

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Check gas port alignment. Stick a small allen wrench in the hole (after taking the plug and piston out) under the gas cylinder and see if it makes it down into the barrel. I think you need to snug the gas lock down a couple of more turns. See how big the gap is between the barrel shoulder and the front band.

Tony.
 

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I would bet you a lot of nickles that when you reassembled your gas cylinder that last time. You let the Gas lock rotate one or two rotations either in or out from its original position which woudl cause your gas cylinder to no longer be aligned with the gas hole in the barrel.... Probbaly the most common mistake.

Point the rifle at the ceiling. Lock the bolt to rear. Insert 1/16th inch allen wrench drill bit or whatever that you have that is about 1/16th in diameter into the small vent hole in the bottom of the cylinder to see if it will pass into the barrel. If it does not pass freely into the barrel you need to turn the gas lock one turn at a time put it back together and repeat until it passes this test.
 

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Back off the lock 90 degrees, whack the cylinder with a rubber mallet (a few times if you're up for it) tighten the lock back down. Sounds like you're a turn or two short and you have a tight fitting gas cylinder (good thing).
 

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Either that or it's possible your gas cyl plug screw is cracked. I say that b/c I'd be curious why it backed out on a new rifle in the first place. SAI usually puts down anything with threads on it farmer tight. As you've been advised, you'll need to do some dis-assembly, alignment, re-assembly, and check-out on the gas system anyway. Look over that plug screw, replace if it shows a crack or missing any metal.
 

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at the sase at bagram in '08 eight m14s were brought in for the exact same complaint as yours. on every one the gas valve was turned off. check this also.
andy
 

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Discussion Starter · #9 ·
at the sase at bagram in '08 eight m14s were brought in for the exact same complaint as yours. on every one the gas valve was turned off. check this also.
andy
Mine is unitized, unless something is broken it should be screwed and glued open. I sure hope it is ok!
 

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Discussion Starter · #10 ·
Thanks for the replies men, they have been helpful and I think I can solve my problem tonight because of them.
 

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ok i don't think we are on the same wave length. on the side of the gas cyl assy is a screw head, it controls the spindle valve that either lets gas pressure from the barrel into the gas cyl through the opening that previous posts asked you to check the alignment of, or rotated 90 deg will turn the gas pressure off completly, as per a grenade launching requirement. the gas cyl being unitized is of no matter to the gas valve. the slot should be in a vertical position when it is in the "on" position. if you try to check the alignment of the gas ports & the valve is in the off position then the 1/16" allen will not travel all the way to the barrel port. hope this helps a little
andy
 

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Discussion Starter · #12 ·
ok i don't think we are on the same wave length. on the side of the gas cyl assy is a screw head, it controls the spindle valve that either lets gas pressure from the barrel into the gas cyl through the opening that previous posts asked you to check the alignment of, or rotated 90 deg will turn the gas pressure off completly, as per a grenade launching requirement. the gas cyl being unitized is of no matter to the gas valve. the slot should be in a vertical position when it is in the "on" position. if you try to check the alignment of the gas ports & the valve is in the off position then the 1/16" allen will not travel all the way to the barrel port. hope this helps a little
andy
I am fairly certain that the manner in which my gas cylinder was unitized makes the spindle valve inoperable. It has two screws through the valve. I took a look at it last night and everything still looked like it was in the correct spot. Maybe someone else will chime in an let me know if that is correct or if I need to look at the spindle valve more closely.

I sure hope it is just my gas cylinder being misaligned like posted above,that would be the easiest fix.

Thanks for your help.
 

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ok, mine was welded a long time ago & my valve still works. please disregard that info then. aslo please post what you find what your trouble turns out to be. thanks
andy
 

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Discussion Starter · #15 ·
My gas cylinder was definitely not aligned properly. I have fooled around with it the past two nights and can't get it to stay in place as my gas lock is now 1/4 turn past dead center before it is tight.

Where is a good place to buy shims and a good pair of castle nut pliers?
 

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Hit up patriot armory 308 for a set of shims.

Castle nut pliers... I have the ones SA Inc. sells, they're great, but a little spendy. I've heard of some others working, however I have no clue what they are.
 

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As far as castle nut pliers, I took a vicegrip clamping style and modified it. It's the type that makes like a square when closed. Just grind the contact points down to the dimension of the notches (can't remeber the measurement due to being at work) they work like a charm. $8.50 at Lowes.
 

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OP, that 1/4 turn is very, very little "out." I think I'd make sure the gas cyl plug screw is clean, threads good, and sound, and just torque it all back together. Shimming could give you a too-tight unwelcome bind on the barrel or have your op rod hitting the back of the gas cyl at the same time it meets the piston's tail. If your unitized front end is screwed & glued, it usually means the barrel band had to be annealed, which means you can work with the band a little to improve closure to the barrel's shoulder if needed. It's the gas cyl lock and plug screw that do the heavy lifting. Just something else to thing about. Good luck.
 

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Discussion Starter · #19 ·
OP, that 1/4 turn is very, very little "out." I think I'd make sure the gas cyl plug screw is clean, threads good, and sound, and just torque it all back together. Shimming could give you a too-tight unwelcome bind on the barrel or have your op rod hitting the back of the gas cyl at the same time it meets the piston's tail. If your unitized front end is screwed & glued, it usually means the barrel band had to be annealed, which means you can work with the band a little to improve closure to the barrel's shoulder if needed. It's the gas cyl lock and plug screw that do the heavy lifting. Just something else to thing about. Good luck.
Everything is and span clean at the moment.

I can get everything aligned again and torque down the gas plug but by the time I get it out to shoot it, it appears to move enough that it won't cycle.

My thought was that the gas cyl lock needs to be tighter than the current alignment with the plug allows to keep the gas cylinder in position. Is that the correct train of thought.
 
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