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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.
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Does a standard ar15 lapping tool work in 6.5 Grendel applications?Comment
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YesComment
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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.Comment
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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.Comment
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What does the process of bedding the barrel intail? I just ordered the wheeler lapping tool and should be doing it soon. ThanksComment
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Awesome thanks it's on order! Really hoping this takes this thing from a paperweight to the hunting rifle I was wishing for!!Comment
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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.Originally posted by Lastrites View Post
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.Comment
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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.Comment
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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.Comment
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I took apart a manufactured upper barrel and receiver yesterday and was surprised at how tight the nut was. I used the Brownells rod to hold the barrel. A 2 foot breaker bar almost was not enough torque. It moved the vise which I had clamped down to my table saw. I had to turn the barrel wrench horizontal and finally got it loose. The old barrel extension was a tight fit and the new barrel extension was also. I torqued the nut to 30 to 40 foot pounds with my 2 foot breaker bar pulled on about 15 to 20 pounds. Good enough for testing. Loctited the scope mount screws.Comment
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I have heard this before, but I can't ever find them in stock. I'm on a bunch of in stock notification lists right now. The Mega uppers are very, very tight and require heat or barrel in the freezer, but I don't like the finish, I think they are coated with something, definitely not just anodized.Originally posted by joedirt199 View PostComment
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The MUR receivers I have are also too loose for my tastes, I'm using green loctite on extension after I assemble and function check.Originally posted by Dave_H View PostComment
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Mine is definitely not too loose. The barrel extension fits, but its tight going in and tight coming out. I'm still planning to bed the barrel.Originally posted by jurassic View Post
ETA: Mine is cerakoted FDE. Maybe that plays a part in how snug it is.Comment
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So has anyone used the wheeler lapping tool and noticed that the lapping face is not a square cut face like it should be. The face that Laps the shoulder on the upper has a taper to it and I don't get why. The face on the barrel that it will be mating to is square. Well I figured to just see how close it was anyways and it appears the upper was pretty damn close (basically started with perfect wearing from the get go). So I'm not anticipating this will cure my accuracy issues but the upper is now lapped, and the barrel is bedded and torqued so fingers are crossed!!Comment
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