Gunsmithing Bedding an AR15 Barrel in the Receiver.

[wilsoncs3980]

Just built my first AR. I used a Rock River Upper, Lower, and BCG. Wilson 24” fluted varmint Barrel with epsilon vg6 brake, SLR gas block, Magpul PRS stock, Strike Industries Strike Rail. When I first put this together I ran into a few problems. The barrel nut was too small for the barrel. About .050” to be exact. Opened up on the lathe. Nut was hard as hell. Fixed that no problem. Problem is the spacers for timing the nutt for the gas tube wouldn’t work either. No way to fix that. Nut timed at 35 ft lbs and the fit between the barrel and receiver was sloppy. Very sloppy. I wasn’t getting a warm and fuzzy about this. Went to the range and dialed it in. Shot like shit. 2 MOA with Federal Gold Medal Match and worse with American Eagle.

Took it back apart and trued the receiver face up. Bedded the barrel with Loctite 620. Lapping the face also solved the timing problem with nut. Ended up with about 70 ft lbs this time. Back to the range. Used same ammo. Shot two 10 shot groups. The American Eagle was .921” and the Gold Medal was .613. No flyers. Pretty sure lapping and bedding is a good thing. At least when the fit between the barrel and receiver is shit. Definitely solved my problem.

 

[FishDr]

I had a very similar experience. It was also with a RRA upper that i replaced a barrel in. The original shot great. The replacement shot terrible. Removed lapped, bonded etc and shoots good. Always something to learn here.

 

[CaptNemo]

I switched all of my upper builds to BCM upper receivers, they are machined a couple of thousaths of an inch smaller on the inner diameter where the barrel seats. You generally have to warm up the receiver to open the bore to seat the barrel extension for assembly.
I modified my lapping tool to work in the BCM dimensions, all of my builds get lapped and warmed up for barrel installation.

 

[natdscott]

And remember that both White Oak and BAT Machine make oversized barrel extensions to solve this very issue.

But uh...if you used a BCM receiver and a WOA extension, you might find it's too much of a good thing.

...unless you have liquid nitrogen on hand....

 

[PatMiles]

Buy an assortment of shim stock in various thicknesses and shim the barrel extension to fit the receiver snugly. It can be a PIA to do but will pay dividends in how the gun shoots.

 

[natdscott]

But Pat, why would you do that in lieu of just using glue?

 

[PatMiles]

I've never been too shiny on gluing a gun together. Yeah, I realize that there is a barrel nut holding the barrel in place but metal on metal on metal just gives me a warm and fuzzy, besides if it is good enough for JP...

 

[wilsoncs3980]

Shims will take up some of the slop but there is always going to be a small amount of play when using them to shim a rod into a hole. Using the epoxy is the superior method, at least until it's time to remove the barrel.

 

[FatBoy]

We face and Loctite all our AR builds. They are all easily 3/4 MOA or better with handloaded 69-80.5gr. It's just a quick, cheap insurance policy. Haven't lapped any but we use mostly PRI, Geissele and KAC barrel nuts, which have plenty of room or holes. No need for anything fancy to get the gas tube lines up right, but you pay for that option.

 

[natdscott]

I've never been too shiny on gluing a gun together. Yeah, I realize that there is a barrel nut holding the barrel in place but metal on metal on metal just gives me a warm and fuzzy, besides if it is good enough for JP...

Cool. But you do realize that NONE of the true accuracy smiths are doing that? Pioneers or otherwise? Wylde, Martin, Medesha, Holliger, Scandale, and White ALL glue(d) as far as I am aware, and I've owned and/or developed loads for a few of those.

I'm fairly certain the armorers behind all the Service Teams still also use glue on the hundreds of match rifles they assemble.

Some of this pedigree are legitimate 1/4-3/8" guns in testing.

I have nothing against JP, but they're using a unicorn procedure.

 

[F23]

Is the general consensus that glue/loctite takes the place of all the various lapping and machining, or is it just the biggest single improvement?

 

[CaptNemo]

I lap all of my upper builds as a standard operating procedure. The way a BCM upper is machined, the loctite is a moot point.
The BCM is within a few dollars of the rest of the "regular" Flat top uppers at retail price. Catch the blem receivers on sale and they are cheaper than everyone elses.