Accuracy fixed.

[LWP]

And yes Lastrites that's a good point about putting the shoe polish ( or other release agent) on the ramp face and inside the feed ramps just encase some of the epoxy made it's way there. That way it could be removed after curing. Good point Thanks

[LWP]

As far as which product shrinks less that's preference. I just think that either product that is used would be better than the loctite method that could heat up and liquefy.

[LWP]

My reason for Marine Tex http://bulletin.accurateshooter.com/2017...dy-speaks/

[Lastrites]

KIWI natural paste is your friend, thin layer let dry and buff, I would likely put polish on the inside just beyond the ext too as well as the lugs of the ext though more will be pushed out and not into the receiver when inserting. Differently not to torque to spec on the nut, I would say a tad over hand tight but not much more and just enough to seat it well. It will certainly take a good rap to break it free once done. Would also suggest having someone assist so one of you could be wiping away the excess as it oozed out. If the day came and you had to break it apart most likely you would be able to just reinsert in the same upper with little effort but it will be a tight fit.

[LWP]

I couldn't agree more on all parts of your suggestions, using two people to preform this task is essential. And applying more paste in the receiver areas would help prevent epoxy mishaps.

[sk8inrj1]

There exists a high temp and high vibration resistant thread locker that is NOT high strength. Its called Rocksett.
From my experience, Rocksett has about the strength of blue locktite, but with heat resistance up to 2,015 degrees F.
If for some reason its stubborn getting apart, you can break it down in water.
This is the thread locker that most silencer companies use in place of crush washers. As far as I know, no silencer company recommends the use of a crush washer with their muzzle adapters.

[Bruw]

To the OP - Out of curiosity, did you reset the barrel prior to the lapping procedure to try and fix the problem? Shooting 8" groups seems like something would have had to be loose. Glad you got it fixed, but struggling to accept that the lapping alone made that big a difference.

[UpstateArcher]

Does a 6.5 barrel require a different size lapping tool than a .223 at-15? I need to order one asap!!

[Bigs28]

No the lapping tool is for the ar15 upper receiver.

[bj139]

To the OP - Out of curiosity, did you reset the barrel prior to the lapping procedure to try and fix the problem? Shooting 8" groups seems like something would have had to be loose. Glad you got it fixed, but struggling to accept that the lapping alone made that big a difference.

The original post mentions 8" groups at 50 yards or 16 MOA. Something was really wrong.

[Bigs28]

The upper was original assembled at an ar manufacturer. That doesn't mean they are prefect but I expected it to be assembled correctly. When I originally took the upper apart to lap the receiver the barrel nut was on very tight and some of the teeth looked a little bent from the torque it was tightened to. Once removed the barrel was pretty loose inside the upper receiver. I believe it was a combination of multiple factors but at the end the only change was lapping and bedding.

[UpstateArcher]

Does a standard ar15 lapping tool work in 6.5 Grendel applications?

[Bigs28]

Yes

[Dave_H]

This is just some general information that might be useful to others. I'm building a rifle (slowly) and am using a Vltor MUR-1A upper receiver. I bought the PT&G lapping tool to use on the receiver before assembly. The tool pilot will not fit the MUR receiver. Vltor advertises the MUR as a "Mil-Spec correct upper with a thicker wall." That definition is accurate. The thicker wall prohibits using the PT&G tool on the MUR receiver. I "assume" that lapping tools made by the other manufacturers would all have the same pilot diameter, but I don't have another one to check. I PM'd LRRPF52 over the weekend to ask his advice. He mentioned that it might be beneficial to post this in the open forum and I just found this thread. So, if any of you have any experience with the MUR receiver, or have run into this issue before, I'd be interested to hear about it. If anyone has an alternative lapping method that might work, I'd also be grateful to hear about that also.

Great thread.

[Lastrites]

Dave, I would suggest having a profession to check it if worried. If I spent that kind of money on an upper I'd likely bed it and go have some fun and see what it would do or have a machinist inspect it and do it with the proper equipment if needed.

[UpstateArcher]

What does the process of bedding the barrel intail? I just ordered the wheeler lapping tool and should be doing it soon. Thanks

[UpstateArcher]

Awesome thanks it's on order! Really hoping this takes this thing from a paperweight to the hunting rifle I was wishing for!!

[Dave_H]

Dave, I would suggest having a profession to check it if worried. If I spent that kind of money on an upper I'd likely bed it and go have some fun and see what it would do or have a machinist inspect it and do it with the proper equipment if needed.

I'm probably going to do just that...bed the barrel extension and the gas block and try it. I have a couple of barrels (a Ballistic Advantage 18" SPR profile with rifle gas, and I just bought a Lilja 319 from another forum member) to try. Hopefully one of them will shoot well enough to not worry about lapping the upper.

I built a rifle (5.56) for my son for his birthday in April. I used a good barrel from a very well known manufacturer. We can't get it to shoot for s--t. It functions flawlessly, but is all over the place as far as accuracy. I'm really disappointed in it and my son has no confidence in it which kills me. We're going to pull the upper back apart and lap it and bed the barrel and gas block and try again. The barrel-to-upper fit was tight (I couldn't fit a .001" shim between them.), but I didn't lap the receiver or bed the barrel. I think I'm going to increase the barrel nut torque a few ft/lbs. also. I hope my results are as good as the OP's.

[bj139]

I had scope mount screws loosen while I was testing my first two builds. The precision seemed good but became worse while shooting. Now I loctite the scope mount screws. I had not had this happen with bolt guns before but the recoil of the AR must be particularly jarring. All connections between barrel and scope reticle must be considered.

[joedirt199]

This is why I always prefer the BCM upper receivers as they have the tightest barrel extension of all receivers I have found. Haven't needed to freeze the barrel and heat the receiver to get them to mate up, just a nice tight fit that can be assembled with a rubber mallet.