Is lapping the upper face worth the trouble?

[ka30270]

I have a few ar's and am about to put together a couple more. I'm curious as to whether lapping the upper face is actually beneficial to accuracy or if it's something that sounds good because it helps on a bolt rifle. Bolt rifles don't have an inch of barrel extension snuggly fitted into the upper to keep things "straight". I'm wondering if a properly mated upper and barrel would even torque it out of alignment if it wasn't completely square. Then you have also removed the anodizing and it could allow corrosion on the connection.

Thoughts? Thanks all

 

[crazymonkey]

Absolutely worth the effort! Most uppers ar 7 series aluminum some are 6 the barrel isn't going to bend but the upper definitely can . Yes you remove some anodize and it can and will cause electrolysis as you're materials are different. I generally use some blue locktite on the threads anyway so I just add some around the flange where the barrel meets the aluminum upper and your all set .I've seen and heard of antiseize being used also .

 

[cajun]

Check it with a square.

 

[quigley257]

If you buy the lapping fixture or borrow one. the procedure is quick and effective. Some uppers require only a light touch to get complete contact while others are quite a bit more out of square. I've seen "name brand' uppers that needed more lapping than the cheap ones. I use the green Loctite to set the barrel in the upper. The 6mm ARC I built using random components and an EABCO accuracy barrel shoots fantastic. I also made a spring loaded 6ARC cartridge to make lapping the bolt and lugs easy. None of these things are hard to do and seem to help with accuracy and consistency. There is a great sticky thread on AR15.com that details all the tips and tricks for building an accurate gas gun. Nearly all these things are doable by the DIY builder in a home shop environment.

 

[crazymonkey]

Check it with a square.

Not the right way to do things as all you'd do is square the face. It's got to be square and perpendicular to the bore . That's what makes it accurate. The lapping tool fits inside the upper bore and then squares the face perpendicular to the bore .

 

[ARlife4me]

I don't waste my time doing it, but then again it's my time. If the outside isn't square then lapping isn't going to help.

 

[cajun]

Not the right way to do things as all you'd do is square the face. It's got to be square and perpendicular to the bore . That's what makes it accurate. The lapping tool fits inside the upper bore and then squares the face perpendicular to the bore .

The tools I've seen are squaring the face of the receiver so it sits square with the shoulder on the barrel. It does have an alignment extension that aligns the tool but it's squaring the face. The extension is just to line the tool up. I guess maybe it's the same thing. Everyone I have checked that is square on the face has shot well.

 

[crazymonkey]

The tools I've seen are squaring the face of the receiver so it sits square with the shoulder on the barrel. It does have an alignment extension that aligns the tool but it's squaring the face. The extension is just to line the tool up. I guess maybe it's the same thing. Everyone I have checked that is square on the face has shot well.

The rifle will probably shoot OK but the bore alignment to the c/l of the upper will be off in what ever direction it pulls the barrel and you are going to counter with scope adjustment to correct. Here's a picture of the lapping tool notice the large dia is to lap the upper face while the smaller dia is inside the upper bore . This address the perpendicular form the bore to the face . It's probably not for everyone but if your going to build why not make it as accurate as possible?

 

[rpol98]

it might not affect accuracy, which will be in your barrel, but it will certainly improve alignment of the receiver bore axis with the barrel bore axis. most noticeable if you are using iron sights.

if the front face isn't perfectly perpendicular to within thousandths or even ten-thousandths, once that barrel nut clamps that barrel to the upper, it should still be solidly mounted, but perhaps slightly askew, cocked to one side or the other, perhaps in the up-and-down plane. Being solidly mounted ensures the accuracy, despite being askew, you just have to make up for it with the sight or scope elevation, windage adjustments.

as long as the barrel is solidly mounted in the upper, your platform accuracy is derived from your barrel, and of course, you ability as a shooter.

 

[ObiWanKannoli]

The best way to fix accuracy issues on an AR is to buy a bolt action

Kidding aside, lapping a reciever to true up the mounting face to the bore can't hurt if done properly however it's not a magic fix.

 

[ka30270]

Thanks everyone, looks like I'll be picking up an upper facing tool

 

[rpol98]

i'd go with either the Brownells lapping tool, or PTG. if you're doing an Aero enhanced, then you have to go with X-Caliber.

I personally wouldn't go with the Wheeler tool, but to each their own.

been doing mine for nine years so far.

 

[Grumpah]

My 2 cents...if you're spending the time and money to accurize your AR, then yes - definately worth the time and effort. Simple as that. I give the effort and my builds have benefitted from the outcome. Just make sure you buy a quality lapping tool.

 

[aschler]

The biggest improvement I've seen from it was a rifle that was stringing badly. Ends up it was stringing away from the high side; after lapping was completed the stringing stopped and the zero moved 2" at 100yds toward the high side.