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Discussion Starter · #1 ·
Gun smith just put a new barrel on and I am getting friction when the op rod is fully rearward, even with the bolt out. The receiver is a 2001 SAI and the new barrel is a 1990's Wilson NM standard weight. My old barrel was a heavy krieger. So Im going from a heavy barrel (which had no binding) to a smaller barrel which now has binding.

I've tried bending the op rod slightly outward (i prob didn't apply enough pressure to do anything out of fear of tweaking it too much) and I also hit the surface on the op rod where it is contacting (near the roller cutout) the receiver with some high grit emery paper to polish it up.

After doing this the op rod doesn't bind as hard but still will not fall forward on its own weight to pass the tilt test.

A few things I am thinking:
1) Check the op rod guide on the barrel, might be out a little. smith said they trued it to the receiver/barrel
2) Hit the receiver with the emery paper to polish the area where its contacting.
3) Shoot it and watch the area for excessive wear. As long as there are no failures to load and the bolt is picking the round up and putting it into battery I may be g2g?
4) Oh yea, take it to a gun smith... but Id like to fix it myself if I can. Id hate to wait a few weeks for some little tweak I can make myself.

Here is the area (in red) I am talking about, this is NOT my receiver
 

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Two things: 1) What did he mean by indexed to the rcvr and bbl? Nothing wrong or irregular about that in concept, but you've got that op rod guide and gas piston tail to account for as well. I don't know if that speaks to your issue but the op rod guide is easily adjusted if need be. 2) Back on the receiver where your red mark runs is a place where the bolt roller can rub and it shouldn't. But you say you don't have the bolt in the rifle. I think I'd put some grease on the forward (round) part of the op rod and grease the bolt roller and put the bolt back in, do the tilt tests some more to see if grease is coming off the op rod in travel or being deposited back near the receiver heel., or both.

May be that your op rod had been, let's say, adjusted to clear and work smoothly with the heavy barrel. Do you have access to another op rod you could try?

Keep us posted, good luck.
 

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Discussion Starter · #4 ·
Who's op rod?
stock SAI

Two things: 1) What did he mean by indexed to the rcvr and bbl?
just meaning "trued up" so its aligned correctly.

the op rod guide is easily adjusted if need be.
care to expand? what methods to adjust it?

do the tilt tests some more to see if grease is coming off the op rod in travel or being deposited back near the receiver heel., or both.
will do, and what would you say if grease was either being deposited or collected by the op rod?

honestly from looking at the wear, the red mark in my post appears to be the only contact/friction point where its binding
 

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MGySgt USMC (ret)
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Believe it or not, there were rare exceptions when an op rod didn't bind with a Standard M14 barrel, but after we replaced that barrel and put the SAME configuration/outside dimension NM "Light" barrel in, the op rod did bind.

What may be happening.

1. With the first barrel in the gun, was the oprating rod aligned on the piston? If it wasn't, that alone could be the reason. The guide might have been placed slightly off center so the op rod did not bind up.

2. The op rod guide is a bit too far to the right when viewed from the rear and that pushes the op rod too much on the right side. That would cause the top of the op rod handle to bind back there on the receiver.

3. Even though you went to a "smaller' barrel, the last inch or so of light, medium and heavy barrels close to the receiver are pretty close to being the same diameter as that is where the breech is located. The "saddle" of the operating rod may be binding on the new barrel. That was common enough on Med Heavy barrels and I can't tell you how many saddles I filed, ground and sanded to get them not to contact the barrel when the op rod was properly aligned with the gas piston.

PLEASE do not grind, file, cut or sand on the op rod lug or op rod channel in the receiver to correct the problem.

If you blacken the curved portion of the op rod saddle with Magic Marker, you may see rub spots where it is hitting the barrel enough to cause this problem. Sanding the op rod where it rubs normally cures that.

If that is not binding and the op rod is centered on the piston, then slightly bending the rear of the op rod should allow it to slide freely.
 

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If you need to move the op rod guide a hair left or right you can do it with a block of wood and a hammer without pulling and replacing the pin. Sometimes the edges of the op rod guide can be a little jagged. A file will clean that up.

OK, the other. SAI has made some receivers off and on that have to be slightly relieved back there to clear the bolt roller. The unwanted contact typically begins under or just behind the rear sight cover. First order of business is to determine whether that's in fact happening and precisely where. Some shooters here have resolved it by kissing the site of the contact with the Dremel tool.

But let me repeat, I'd try a good-condition USGI op rod before I reached any conclusions. The geometry of your SAI op rod's travel may have been fine with the hvy bbl and its op rod guide, but that doesn't necessarily equate to in-spec. I KNOW your GI contour Wilson barrel, correctly indexed, will work good with a HRA, WRA, SA, or TRW op rod because I've used several of those barrels and op rods in combination over the years.
 

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Discussion Starter · #7 ·
wow thanks for the reply's gentlemen. GI1

1. With the first barrel in the gun, was the oprating rod aligned on the piston? If it wasn't, that alone could be the reason. The guide might have been placed slightly off center so the op rod did not bind up.
The gun started with a scout barrel. Funny, I do recall the op rod being slightly off center as it hits the piston.

2. The op rod guide is a bit too far to the right when viewed from the rear and that pushes the op rod too much on the right side. That would cause the top of the op rod handle to bind back there on the receiver.
can i give it a few love taps with a rubber mallot? or do i have to remove the pin?

PLEASE do not grind, file, cut or sand on the op rod lug or op rod channel in the receiver to correct the problem.
i understand, but to be clear i only polished a small area on the inside of the op rod. basically the part that is contacting the receiver. i have not touched the lug or channel.

If you blacken the curved portion of the op rod saddle with Magic Marker, you may see rub spots where it is hitting the barrel enough to cause this problem. Sanding the op rod where it rubs normally cures that.
i looked at that actually last night and i do not see any wear in that area, however i do recall it being tight... i dont think it would pass a paper test. so i can sand down the saddle of the op rod if its contacting the receiver?

If that is not binding and the op rod is centered on the piston, then slightly bending the rear of the op rod should allow it to slide freely.
knowing my original barrel had the op rod guide tweaked slightly off-center, would you recommend I bend the op rod and keep the guide "true" to the piston? or tweak the op rod guide?

If you need to move the op rod guide a hair left or right you can do it with a block of wood and a hammer without pulling and replacing the pin. Sometimes the edges of the op rod guide can be a little jagged. A file will clean that up.
noted on the jagged guide. its a new one from brownells, Ill give it a look

OK, the other. SAI has made some receivers off and on that have to be slightly relieved back there to clear the bolt roller. The unwanted contact typically begins under or just behind the rear sight cover. First order of business is to determine whether that's in fact happening and precisely where. Some shooters here have resolved it by kissing the site of the contact with the Dremel tool.
this bolded part sounds like what i have. with three options (1) tweak op rod guide, (2) bend op rod, (3) relieve the contact point (least favorable option). Im going to start with #1 i suppose

But let me repeat, I'd try a good-condition USGI op rod before I reached any conclusions. The geometry of your SAI op rod's travel may have been fine with the hvy bbl and its op rod guide, but that doesn't necessarily equate to in-spec. I KNOW your GI contour Wilson barrel, correctly indexed, will work good with a HRA, WRA, SA, or TRW op rod because I've used several of those barrels and op rods in combination over the years.
good advice, but i dont think i want to take it... yet
 

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MGySgt USMC (ret)
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The gun started with a scout barrel. Funny, I do recall the op rod being slightly off center as it hits the piston.


can i give it a few love taps with a rubber mallot? or do i have to remove the pin?
Without seeing the rifle in person, I have to advise caution at first. Did your gunsmith knurl or epoxy/Loctite the op rod guide? You can normally see evidence of it had he done either. If it was glued, you probably can not move it without harming the op rod guide.

If it was not glued/Loctited, then you most likely can tap it over to the side a little bit even with the pin in place. However, I am not a fan of moving the op rod off center to the piston just to get the op rod to slide freely. If the op rod is centered on the piston, then I would look to other areas to loosen up the op rod fit.


i understand, but to be clear i only polished a small area on the inside of the op rod. basically the part that is contacting the receiver. i have not touched the lug or channel.
Good.

i looked at that actually last night and i do not see any wear in that area, however i do recall it being tight... i dont think it would pass a paper test. so i can sand down the saddle of the op rod if its contacting the receiver?
I would blacken the whole surface of the op rod saddle where it fits under the barrel chamber and just behind the op rod tube. Then slide the op rod back and forth maybe 10 times. Then take the op rod off and see where it rumbs the barrel. Then file/grind/sand that area of the op rod guide where there are rub marks. Then reblacken the surface and try again. You sometimes have to do this four or five times (or more) to relieve the rubbing - just be careful not to go hog wild and cut too much metal off the surface of the op rod.


knowing my original barrel had the op rod guide tweaked slightly off-center, would you recommend I bend the op rod and keep the guide "true" to the piston? or tweak the op rod guide?
I always start with the op rod centered on the piston. Then relieve rubbing in the saddle, then bend the rear end of the op rod a bit - if necessary.
 

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OP, you've lost me. I thought you said you're going from a heavy match barrel (you said Krieger) to a standard Wilson NM barrel. But then you said the rifle started with a scout barrel. ?????

Members, incl Gus Fisher, took the time to try to help you. You got valuable tips. Now, if you've swapped from a short SAI factory barrel (18.5") to a standard-length (22") barrel, it's entirely possible your op rod was manipulated (i.e., bent) at the factory to some degree to enable SAI to get it out the door.

Whichever it was, I suspect you'd benefit by trying a known original spec M14 op rod.

Out.
 

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Discussion Starter · #10 ·
I was able to remove a little bit from where it was rubbing on the op rod. You can see it starting about half way up on the right side and tapering off as it goes to the left. This was the contact point that was rubbing. Tilt test passed!


bd, it started as a scout, then i went heavy barrel, now im doing a standard weight barrel... final answer :)
 
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