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Discussion Starter · #1 ·
Hey guys,

My dad purchased an M1A Loaded rifle from the PX here on TFL. He recieved it yesterday so he brought it over to my place to show me. Him being new to the M1A (I'm new as well but have owned one for a few months now) he had me show him how to take it down, clean it, etc.

Well while looking it over I realized that the op rod is not being stopped by the piston. It stops about .015 short, and is stopping on the bolt roller instead.GI8

I have read about this issue before on here so I knew to look for it. The gas plug is tight, and the front band and gas cylinder are tight against the barrel flare. I varified with a few taps from a rubber mallet.

Also the gas cylinder and front band have been unitized with the screw method, supposidly by a well known smith in AZ. Looks like a really clean job.


I put the piston from my rifle in and it closed the gap to about .010. My piston actually measured about .010 longer on a micrometer. Kind of weird.

What can we do to remedy this? I can't think of anything. Can he send it back to SAI under warranty with the gas cylinder unitized? He is pretty bummed to say the least.

Also the gas lock tightens at about 6:15,but shimming is out of the question with the piston falling short I would think.

Thanks for the help!
 

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Have you function fired it yet? Does the bolt close fully into battery position? It might be posible that although out of spec it is fully functional. Did the previous owner disclose any problems he has had?. If he didnt and it doesnt function properly I would consult him on a possible refund/return before trying to send it in for warrenty work, If he's an honest seller Im sure it wont be a problem.
 

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Discussion Starter · #3 ·
Have you function fired it yet? Does the bolt close fully into battery position? It might be posible that although out of spec it is fully functional. Did the previous owner disclose any problems he has had?. If he didnt and it doesnt function properly I would consult him on a posible refund/return If he's an honest seller Im sure wont be a problem.
Previous owner said it functioned fine and was very accurate. I have no doubts that it will function fine as is, but long term having the op rod stopped by the bolt roller will cause pre mature wear and damage as well as hammer the piston with every shot. I can't figure out how to move the piston back when the gas cylinder is already flush with the barrel and front band and the gas plug is tight. Maybe an adjustable gas plug would move the piston further back?
 

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Previous owner said it functioned fine and was very accurate. I have no doubts that it will function fine as is, but long term having the op rod stopped by the bolt roller will cause pre mature wear and damage as well as hammer the piston with every shot. I can't figure out how to move the piston back when the gas cylinder is already flush with the barrel and front band and the gas plug is tight. Maybe an adjustable gas plug would move the piston further back?
The piston has doubtless been trimmed at some point; the only way to bring the piston back into contact with the op rod is to replace the piston with a new or untrimmed used one.
 

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an adjustible gas plug is the only thing I can think of as well, I dont know where would be a good place to pick one up. even if it does function good I wouldnt be comfortable with it stopping on the bolt roller either, I cant imagine that holding up for very long. why would someone trim the piston? would that be an easy way to compensate for an out of spec part? Iv never heard of that before but it would make sense
 

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Discussion Starter · #6 ·
The piston has doubtless been trimmed at some point; the only way to bring the piston back into contact with the op rod is to replace the piston with a new or untrimmed used one.
I hadn't thought of that possibility. Isn't that a method to increase "dwell time" ? Even so, my new piston still fell short by a hair. Not sure what's going on.
 

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The cylinder is seated against the barrel shoulder and the gas lock can't be turned any further? If so the plug and piston would be the first suspects. Does it look like the tail has been machined at all? Same with the face of the plug? I'd start with those two. Having the bolt roller stop the op rod is really bad juju.
 

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My Springfield needs to have the gas cylinder lock on the right way or a small gap is created in between the front band and the rib on the barrel that it is supposed to sit on. Check to make sure that there is no gap there. If there is, try flipping the gas lock around and retighten it.
 

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At least a new gas plug and maybe a new piston, tell your dad not to worry this is an easy fix. Also check the screws used to unitize the unit. Make sure that they are screwed in all the way. There should not be any space between the front band and the gas cylinder. Post some pictures if you can especially of the unitized parts of the cylinder and the plug and piston. Worst comes to worst you can change out the cylinder it's no big deal. The loaded is a great rifle, this to shall pass.
 

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The cylinder is seated against the barrel shoulder and the gas lock can't be turned any further? If so the plug and piston would be the first suspects. Does it look like the tail has been machined at all? Same with the face of the plug? I'd start with those two. Having the bolt roller stop the op rod is really bad juju.
Yep... my thoughts too. Since another piston didn't bring it in, I would swap the plug to see if that made a difference. If not, it has to be an out of spec, way thick gas lock. Reducing it's thickness would bring the plug closer for the op rod to hit the piston before slapping into the roller. I'd measure it 10 times before cutting anything. Only because I have more than once cut something 10 times and it'd STILL be too short. So bee careful.

Good luck with it!!
 

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...Maybe an adjustable gas plug would move the piston further back?
I agree with everyone else that a different gas plug should be tried since there's always the possibility yours was shortened to change dwell (I tried that but marked the plug so I'd know which was which without measuring). But an adjustable gas plug doesn't adjust in length; it vents some of the gas to reduce pressure applied to the piston and that's done by changing the size of the vent and/or the volume of the space inside the plug.
 

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Don't overlook the obvious.

You have a unitized gas cylinder. That doesn't mean that the gas lock has been set correctly.

The purpose of the gas lock, is to position the gas cylinder so that the hole in the barrel is aligned with the hole in the gas cylinder. That's how the gas enters the gas cylinder, and functions the rifle.

Make sure those holes line up!

You can lock the bolt to the rear, so that the piston slides back with gravity, and drop a pin or drill bit in the vent hole. If it is visible through the muzzle, the holes are lined up.

If the pin won't go through, you need to tighten the gas lock.
 

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How about contacting the seller and ask if this was something that was noticed while they owned it? If so, is there a reason behind it?
 

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Discussion Starter · #15 ·
thanks!

Thanks for the help! He is bringing the rifle by again on Tuesday so I will look into it closer then. Now I have some ideas to work with! He is also attempting to contact the seller. Thanks again! Ill post an update when we figure it out.
 

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Good luck. I hope it's something simple. It's the kind of head-scratcher that's tough to diagnose at a distance. Sometimes issues come up because we've got these combinations of GI parts and commercial parts. I guess we're lucky we don't encounter more cases of misfit than we do.
 

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I had a lock that tightened to 3 o'clock and 2 o'clock when flipped. When I backed it off the op rod lost contact with the piston (the lock has very coarse threads). So I went on a quest for the perfect lock, I ended up buying 5 and got one that locked up perfectly with my setup. Stopped by hand at 4:30 and wrenched tight to 6 o'clock. When installing the plug the piston made contact with the plug for the last turn by hand (considered great for dwell time) then less than 1/4 turn to torque it to 15 ft-lbs. The threads on the plug are VERY fine, I'm guessing 1/32 but they may be 1/64, regardless that's not much per turn either way.

If you find the gas cylinder isn't seated to the shoulder and it's off by over half a turn you may want to look into getting some different locks to try. Plus side you can usually sell them pretty easy.
 

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Discussion Starter · #18 ·
Update

Had the rifle dropped off at my place and I got around to looking at it last night. I went so far as to swap gas cylinders, the piston, and gas plug trying to find the problem. Couldn't close the gap. The op rod is still being stopped by the bolt roller. I gave Springfield a call this morning and after having to call back 4 times to finally speak with a technician, they requested that I send the rifle back in for repair. I made sure to inform them that it has a unitized cylinder (done by Ted Brown I have since learned). I also told them that the problem isn't with the cylinder because I tried another unmodified SAI cylinder to no avail and to please keep it on the rifle, even if they replace other parts. So we'll see what happens, the rifle is on it's way...
 

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things

Sounds as though you narrowed it down to an out of spec barrel, or a very, extra large, barrel ring on the receiver....good job !
 

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In this case-gas lock

This is one of those rare cases where I would remove enough off of the gas lock to allow the gas plug to push the piston out enough to pre load the op rod with no gap. if you are using a unitized gas cylinder, just take enough off to take up the gap.

Other options may be limited depending on where the gas port lines up. Is it centered, forward or back?

The most likely problem is simply the roller position on the bolt? Is this a SAI bolt? It's probably the bolt or the gas cylinder shoulder being slightly further forward than it should be or a combination of both.

Have you tried another bolt to see if that changes the gap? How about another op rod? I've seen op rods without the proper clearance, which causes it to bind on the roller.

The easy fix, that won't hurt your dwell time is to take some material off your gas lock. Since you have a gap between your piston and op rod, and a unitized gas cylinder, you can take just enough off to eliminate the gap. A slight pre load is desirable. Ever so slight!

Good luck!
 
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