Squared Upper

[65Whelen]

I picked up an upper receiver lapping tool and since winter came a little early and I already have some extra time on my hands I gave it a try. I was surprised by the results.

Quite a difference between receivers, the receiver with complete contact originally had about 80% contact, then I finished it with the lapping tool. The other receiver I just hit it with the lapping tool to see how far out it is.

Just wanted to share my results with the Horde. So, if your considering an upper receiver lapping tool, I recommend it.

http://www.brownells.com/gunsmith-tools-supplies/rifle-tools/receiver-tools/ar-15-m16-upper-receiver-lapping-tool-prod20220.aspx?avs|Newsletter_1=Black%20Rifle%20Tools%20and%20Supplies

[LRRPF52]

I would also suggest orienting the work vertically so you don't bias the cutting based on gravity away from the BCG tunnel.

A good way to go is to get undersized uppers in the tunnel opening, with machined square faces as part of the process, then anodize, then thermo-fit the barrel extension into them.

For barrels, the extensions need to be held to certain QC specs, trued and squared, with a barrel made by someone who can keep the bore concentric to the OD.

[Wheelhorse]

I bought a 5.56 carbine from a guy at a gun show. When I shot it, the rear sight had to be moved all the way to the left to get the windage correct. When I took it down and started lapping the receiver face, it was clearly high on one side. I finished the lapping and put the rifle back together. Anyone want to guess where my rear sight is at now?
As stated above, the tool should be operated vertically with everything very clean and well lubed.
Yes, I'm a believer.

[just_john]

Have been assembling a "Christmas Surprise" for younger grandson and trued the upper. It was visibly out of square when I started. Am going back to square up the others that I have built. In this day of incredibly consistent CNC processes, it is hard to imagine that there would be this kind of tolerancing problem.

[am4966]

Dang it now I have to get another item! For my builds, but it will pay off in the end. So question after you lap the upper and lets say the barrel extension is loose what do you use to bed the barrel? Loctite? If so which on?

Thanks for any and all info

[Wheelhorse]

Dang it now I have to get another item! For my builds, but it will pay off in the end. So question after you lap the upper and lets say the barrel extension is loose what do you use to bed the barrel? Loctite? If so which on?

Thanks for any and all info

I haven't assembled as many as most of you guys, but have yet to find a barrel extension loose. Does this really happen? Seems to me that might be a issue for the company that made the barrel to resolve.
I remembered something else. The Brownells tool was out of stock when I was looking for one so I bought the Wheeler kit. It came with what seemed to be a water based abrasive. I had a can of this on hand http://www.use-enco.com/CGI/INSRIT?P...PMAKA=391-5874.
It is grease based and I thought it might stay in place better, so that is what I used. I surely didn't want any of this migrating down in the receiver while lapping.
I don't understand how these receiver faces get off as they do. The only one I've found really bad, was on the carbine bought from the gun show.
I owned a Colt H Bar 25 years ago on which the rear sight had to be moved all the way over to get it zeroed. That gun was sent back to Colt because of it. They said it was "in spec" and refused to do anything about it. I don't know that was the problem, but I sure would like to have it back now. I would find out.

[LRRPF52]

A lot of uppers are out of square as the norm. Parts suppliers and rifle builders don't often care about the pursuit of common decency when making guns, so as long as it looks like a recognizable part, it's good enough for them.

Yes, you can bed with Blue Loc-tite, which is probably the most common method.

I have an old Colt SP-1 slickside upper that is perfectly square when I checked it with the tool. I don't lap if the face is square already. Extension tunnels come in varying sizes, as do barrel extensions. This can manifest in different types of fitting, tight or loose, depending on the how the tolerances stack.

Barrel nuts and extensions are out of square often as well.

[customcutter]

I haven't assembled as many as most of you guys, but have yet to find a barrel extension loose. Does this really happen? Seems to me that might be a issue for the company that made the barrel to resolve.
I remembered something else. The Brownells tool was out of stock when I was looking for one so I bought the Wheeler kit. It came with what seemed to be a water based abrasive. I had a can of this on hand http://www.use-enco.com/CGI/INSRIT?P...PMAKA=391-5874.
It is grease based and I thought it might stay in place better, so that is what I used. I surely didn't want any of this migrating down in the receiver while lapping.
I don't understand how these receiver faces get off as they do. The only one I've found really bad, was on the carbine bought from the gun show.
I owned a Colt H Bar 25 years ago on which the rear sight had to be moved all the way over to get it zeroed. That gun was sent back to Colt because of it. They said it was "in spec" and refused to do anything about it. I don't know that was the problem, but I sure would like to have it back now. I would find out.

WH,

When he said the barrel extension was loose, he meant the fit was loose to the upper. Not that the extension was loose on the barrel. As LRRPF52 said, you can bed the extension to the upper by using Blue Loc-tite. Just remember you'll have to heat with a heat gun in order to remove the barrel from the upper, if you ever have too. Don't use a torch as you can easily overheat and ruin the Rc hardness of the Al upper.

[Wheelhorse]

I think this product might be a better choice to fill the looseness in the receiver to barrel extension fit.
It's made specifically to fill the void in machined parts.

http://www.loctite.com.au/3320_AUE_HTML.htm?nodeid=8802647703553

[65Whelen]

I think this product might be a better choice to fill the looseness in the receiver to barrel extension fit.
It's made specifically to fill the void in machined parts.
http://www.loctite.com.au/3320_AUE_H...=8802647703553

But is disassembly going to be a problem? With Blue Loctite you can heat it up with a hair drier and the barrel can be removed, is that possible with the 660 Quick Metal?

[montana]

I just helped mount 2 barrels for a friend using blue loctite a few days ago. He had YHM uppers and they were perfectly square unlike many I have used. I have removed many barrels using blue loctite with out any problems. Use a little heat and it will wiggle loose. Don't over apply the blue loctite, just a small film around the outside of the barrel extension is plenty. I watched a video of some guy over applying it and it squirted out everywhere, completely unnecessary. Blue loctite works fine and is easy to remove when needed.

[Nukes]

I just helped mount 2 barrels for a friend using blue loctite a few days ago. He had YHM uppers and they were perfectly square unlike many I have used. I have removed many barrels using blue loctite with out any problems. Use a little heat and it will wiggle loose. Don't over apply the blue loctite, just a small film around the outside of the barrel extension is plenty. I watched a video of some guy over applying it and it squirted out everywhere, completely unnecessary. Blue loctite works fine and is easy to remove when needed.

So... YHM has pride in their products.

What other shops sell receivers that are squared off the shelf?

[montana]

So... YHM has pride in their products.

What other shops sell receivers that are squared off the shelf?

SI and Alexander Arms were the only other upper receivers I have used that didn't need lapping. I'm sure there may be other higher priced uppers that I haven't used.

[Sniper338]

Yall got me thinking... i didnt square my upper receiver lugs... but it shoots lights out so im having a hard time considering messing with it..

[montana]

Yall got me thinking... i didnt square my upper receiver lugs... but it shoots lights out so im having a hard time considering messing with it..

If it ain't broke don't fix it.