Upper receiver Lapping

[Stone]

Are any of you guys Lapping your uppers before assembly? It trues up the receiver to the barrel and is supposed to make the rifle a lot more accurate. This is a big thing over on the 68 Forum. Wish I had known about this before I completed my last build. There is a video on the linked page.

http://www.brownells.com/gunsmith-to...prod20220.aspx

[GaSwamper]

I just started not too long ago. One I could tell a little difference but the other was already a .5'' rifle so hard to tell. I do like the way the barrel seats and mil-spc nuts line up once it is lapped.

[GOST]

CIV Tactical offers blue printed uppers for $120.

https://www.civtactical.com/shop/ind...roducts_id=101

[GaSwamper]

CIV Tactical offers blue printed uppers for $120.

https://www.civtactical.com/shop/ind...roducts_id=101

Yes but then you won't get lapping compound allover you, your clothes, and bench.

[Naytwan]

CIV Tactical offers blue printed uppers for $120.

https://www.civtactical.com/shop/ind...roducts_id=101

That's not a bad price. I gotta wait to build my last lower though want to build a SPR.

[FortTom]

Are any of you guys Lapping your uppers before assembly? It trues up the receiver to the barrel and is supposed to make the rifle a lot more accurate. This is a big thing over on the 68 Forum. Wish I had known about this before I completed my last build. There is a video on the linked page.

http://www.brownells.com/gunsmith-to...prod20220.aspx

Unless you have a totally screwed up receiver, I seriously doubt that lapping the upper alone is going to make your rifle "a lot more accurate". Achieving any appreciable amount of accuracy in most rifles is the result of a lot of things, a quality match grade barrel, custom trigger, ammo hand loaded to that one specific rifle, etc..etc..

I would also ask this question. How do you know that your upper receiver isn't true? Are you using a dial indicator to determine run out? Are you taking before and after measurements? Are you using a dial indicator to check the face of the barrel to ensure that it's true also? Have you taken into account the "crush factor" of torqueing your barrel nut down?

I think that unless you have access to a machine shop, and address a lot of issues, that affect accuracy, save your money and put it into high quality parts to begin with. CNC machines today can easily push out receivers with tolerances of .0001 (one ten thousands) of an inch, at a given temperature. I doubt that hand lapping will give you any advantage over that.

All that being said, it may give you a minor advantage, if you start the whole project as a highly accurate match grade rifle, with all components geared towards accuracy, to start with.

[Deadwing]

My rifles are capable of shooting far better than i am. So even if lapping did improve accuracy, and i'm not sure it does, until my skills as a shooter get a whole lot better, there'd be no point in lapping the receiver for me. Even then, i doubt i'd spend my time/money on it.

[SINNER]

I agree with what Fort Tom said 110%.


Have to love the gun industry. Creating solutions to problems that can not exist. I has no bearing on accuracy at all if the front of the receiver extension is "not true". True to what? The rail? The bolt face? The barrel on AR receivers is aligned by the receiver's bore that the barrel inserts into, not the face of the extension. The fact that people actually believe they can improve on a CNC machined part with valve grinding compound and cordless drill humors me to no end. Almost as much as the fact that the aluminum will conform to the barrel flange once you exceed 25-30 ft lbs of torque regardless of how it's dressed before assembly. I have personally seen 2 uppers ruined by people removing to much material causing the barrel extension to protrude too far into the receiver. One the gun grouped worse from the extension damaging the bullet on it's way into the chamber. One was so bad it would not feed as the bullet caught on the extension.

If anything that kit shown above will decrease accuracy by also removing material where it actually matters. The extension bore to barrel extension interface.

[Stone]

Yep, good post Tom and great points. I agree that the words "A lot more accurate" was a little to severe.

[Stone]

CIV Tactical offers blue printed uppers for $120.

https://www.civtactical.com/shop/ind...roducts_id=101

Thanks for posting this. It does kind of create the question of "even though its blue printed and well machined, they still do the lapping anyways" Since so much is going into quality control why do they still lap it afterword's? Unless that part of the UR is hard to get to super tight tolerances.

[Stone]

I agree with what Fort Tom said 110%.


Have to love the gun industry. Creating solutions to problems that can not exist. I has no bearing on accuracy at all if the front of the receiver extension is "not true". True to what? The rail? The bolt face? The barrel on AR receivers is aligned by the receiver's bore that the barrel inserts into, not the face of the extension. The fact that people actually believe they can improve on a CNC machined part with valve grinding compound and cordless drill humors me to no end. Almost as much as the fact that the aluminum will conform to the barrel flange once you exceed 25-30 ft lbs of torque regardless of how it's dressed before assembly. I have personally seen 2 uppers ruined by people removing to much material causing the barrel extension to protrude too far into the receiver. One the gun grouped worse from the extension damaging the bullet on it's way into the chamber. One was so bad it would not feed as the bullet caught on the extension.

If anything that kit shown above will decrease accuracy by also removing material where it actually matters. The extension bore to barrel extension interface.

Ultimately the shoulder of the BE rests against the receiver face, and if that is out of square it will advance that un-trueness out to the end of the barrel and (exaggerate it because now distance is added to the equation) causing it to be tilting left, right or up and down. Granted that most iron sights will have enough adjustment to compensate for this. Unless a guy is looking to shoot half inch groups or tighter,at the end of the day it may not be for everyone.

[BoilerUp]

Ultimately the shoulder of the BE rests against the receiver face, and if that is out of square it will advance that un-trueness out to the end of the barrel and (exaggerate it because now distance is added to the equation) causing it to be tilting left, right or up and down. Granted that most iron sights will have enough adjustment to compensate for this. Unless a guy is looking to shoot half inch groups or tighter,at the end of the day it may not be for everyone.

This is what I concluded from looking at upper receiver lapping, too. It doesn't increase accuracy, per se, but if there was an alignment issue you could run out of windage or elevation on your sights/optics (i.e., essentially your barrel is pointing a slightly different direction than the rail on your receiver). This is pretty rare and generally indicates a defect or blemish on the upper, but lapping can solve this problem. My take-away is to visually inspect the receiver face for a smooth finish and visually inspect for gaps between the face and BE upon installation. If it looks uniform you are probably good to go. IF you see obvious variation or run out of windage/elevation when sighting in, you might want to consider lapping. But that is almost certainly a rare exception.

But, I get why some people might choose to do a light lapping everytime just to be sure. It doesn't appear to take much effort and probably makes the builder feel better. :)

[Will@AR15Hunter]

I do on my accuracy rigs, or if there seems to be an issue with the barrel extension/upper fit.

I took a stripped upper and a picture of the Brownell's tool to my buddy, who owns a machine shop, and he made me one up. Works great with a little valve lapping compound. Takes only a few minutes.