"Accurizing the AR-15"

[bfoosh006]

Thanks for bringing this up, I have always contemplated doing these two steps, and I am getting ready to re-barrel one of my primary rifles and will probably do the lapping, and should also probably will do the glue.


I don't know, but both of the two things I would consider are cheap and look easy, and I am planning to tear it apart anyway, so I will probably do the experiment.

I am a true believer in the "True n' Glue".

FWIW, the various lapping tool's , I have tried, have certain uppers they worked well with.

Brownells, thermal fit uppers like BCM
PTG , used to work well with non-thermal fit uppers.. I say used to , because they sell to different sizes now.
The Caldwell ( cheap ) lapping tool, was such a poor fit, I could see doing more damage than good.

I also do not place the upper in a vice, while lapping. I turn the upper vertical and use a low speed setting cordless drill. That way I can feel any "odd" binding. Be sure to lube the lapping tools shaft.

FWIW... and while far from scientific, here is a PSA 20" OEM barrel 6.5CM before and after TnG ( True and Glue ). The thread is a little choppy.... but I don't write for a living. Lol
Not every factory load responded well to the TnG, but... many did group far better after.

And the odd ball fliers seemed to occur less often.

Enjoy the read...

https://www.ar15.com/forums/industry...s-/301-285762/

[Wake27]

I've never tried any of it but d. Wilson does offer bedding/shimming and receiver truing services.

[stomridertx]

I've adopted this method of building my uppers, but instead of using retaining compound I use stainless steel shim stock to tighten the fit of the barrel extension into the upper. If I were building a new upper today, I'd spend the money on a VLTOR MUR, BCM, or Sons upper receiver that would allow the thermal fit method. I also true the receiver with a lapping tool.
In my experience, lapping the receiver will minimize the windage adjustment on the optic or irons when zeroing. If you have an upper where you have to make an extreme windage adjustment on the rear BUIS, lapping the receiver might be the ticket for you.
I did witness firsthand an accuracy increase from tightening up the barrel extension fit to the receiver. My main and favorite AR is a BCM 16" upper with a cold hammer forged barrel purchased around 2012, before BCM adopted their thermal fit specs and were just making Milspec upper receivers. I was getting around 3 MOA accuracy with M193 ammo on this upper. As time went on and I got deeper into the hobby of putting these things together, I wanted to change the handguard out and had read about the different ways to "accurize" the AR. When I took it apart, the fit was akin to a hotdog in a hallway. I lapped the receiver with a wheeler tool and used 0.003 stainless shim stock to achieve a really tight fit of the extension. This rifle now shoots M193 1.5 to 2 MOA, and shoots Speer Gold Dot LE 62 GR .223 sub-MOA. I don't think a huge increase like this is typical, and some of that very well could be me being a better shooter now than when I first started out. I'm a full on nerd about zeroing and get the rifle really stable using bags now.

[bfoosh006]

I've adopted this method of building my uppers, but instead of using retaining compound I use stainless steel shim stock to tighten the fit of the barrel extension into the upper. If I were building a new upper today, I'd spend the money on a VLTOR MUR, BCM, or Sons upper receiver that would allow the thermal fit method. I also true the receiver with a lapping tool.
In my experience, lapping the receiver will minimize the windage adjustment on the optic or irons when zeroing. If you have an upper where you have to make an extreme windage adjustment on the rear BUIS, lapping the receiver might be the ticket for you.
I did witness firsthand an accuracy increase from tightening up the barrel extension fit to the receiver. My main and favorite AR is a BCM 16" upper with a cold hammer forged barrel purchased around 2012, before BCM adopted their thermal fit specs and were just making Milspec upper receivers. I was getting around 3 MOA accuracy with M193 ammo on this upper. As time went on and I got deeper into the hobby of putting these things together, I wanted to change the handguard out and had read about the different ways to "accurize" the AR. When I took it apart, the fit was akin to a hotdog in a hallway. I lapped the receiver with a wheeler tool and used 0.003 stainless shim stock to achieve a really tight fit of the extension. This rifle now shoots M193 1.5 to 2 MOA, and shoots Speer Gold Dot LE 62 GR .223 sub-MOA. I don't think a huge increase like this is typical, and some of that very well could be me being a better shooter now than when I first started out. I'm a full on nerd about zeroing and get the rifle really stable using bags now.

FWIW... the SOLGW upper is also a MUCH snugger fit on every lower I tried.
IMHO a tight fit between the upper and lower makes it far easier to wield the AR more consistently.

BCM lower was TIGHT. As in had to "slap" the 2 parts apart.
Colt was inbetween TIGHT and snug.
SanTan lower was snug.
Rainer Arms lower was snug.
PSA was a much better fit, compared to PSA uppers.

I tried the SOLGW upper on other make lowers, but I don't remember which ones.

[DDTSGM]

I also true the receiver with a lapping tool. In my experience, lapping the receiver will minimize the windage adjustment on the optic or irons when zeroing. If you have an upper where you have to make an extreme windage adjustment on the rear BUIS, lapping the receiver might be the ticket for you.

I use a Brownell's lapping tool and have noticed the same thing which I thought was the whole point of lapping.

I pretty much use nothing but BCM blem uppers. I tend to use Green Mountain Barrels when they have what I want, but have also used others. Fit to receiver is snug, but I've never had to thermal fit. Is that unique to the blem uppers?

[stomridertx]

I use a Brownell's lapping tool and have noticed the same thing which I thought was the whole point of lapping.

I pretty much use nothing but BCM blem uppers. I tend to use Green Mountain Barrels when they have what I want, but have also used others. Fit to receiver is snug, but I've never had to thermal fit. Is that unique to the blem uppers?

Making the barrel stick out of the receiver as straight as possible to fix extreme windage adjustments is the whole point of lapping. I pointed it out to answer TWR's question earlier as I think the original intent of it seems to have been lost over time and has deteriorated to:
"Dude, you should totally lap your receiver!"
"Why?"
"Cuz accuracy bro!"
It's honestly probably not worth the time on an upper that isn't getting a rear iron sight. Scopes and red dots have plenty of adjustment and windage doesn't get dialed to the same degree as elevation. I was able to fix a friend's retro AR build with lapping though as his carry handle rear sight adjustment was damn near all the way to the left and he hated it. Lapping moved it close to center on zero. As armorer level tasks go, lapping is easy.

[TWR]

Nearly every off center rear sight that I’ve seen, in person and on the wild wild net, has been to the left. Before the lap tool became popular, it was a hammer to the front sight base that rotated the sight back in line. Seems odd that the rear was always to the left. Never bothered elevation either.

I have a cheap upper that The rear sight is to the left. I thought about this when it was mentioned lapping fixes the issue. After closer examination, my rail is canted. I’m gonna buy a lap and try it but I’m still not understanding how a hand held tool can be the cure when I go to rather great extremes to square things up on my lathe. I’ll give it a try but first I will see if the upper is square to begin with.

Please don’t take this as arguing, my mind just works this way.

[WobblyPossum]

We have a BCM ELW-F 14.5” with the original Magnesium KMR rail that I purchased used about 7-8 years ago. It’s a great gun but I’ve zeroed it with two different sets of iron sights and the rear is always pretty far to the left. It shoots just fine but I never thought about the upper not being square, causing the barrel to actually be tilted.

[stomridertx]

Nearly every off center rear sight that I’ve seen, in person and on the wild wild net, has been to the left. Before the lap tool became popular, it was a hammer to the front sight base that rotated the sight back in line. Seems odd that the rear was always to the left. Never bothered elevation either.

I have a cheap upper that The rear sight is to the left. I thought about this when it was mentioned lapping fixes the issue. After closer examination, my rail is canted. I’m gonna buy a lap and try it but I’m still not understanding how a hand held tool can be the cure when I go to rather great extremes to square things up on my lathe. I’ll give it a try but first I will see if the upper is square to begin with.

Please don’t take this as arguing, my mind just works this way.

I don't think the receivers are actually out of spec when the barrel isn't perfectly straight if it's a quality manufacturer, it's the anodizing that gets applied a tiny bit uneven and the lapping tool just evens it out. I saw a video of someone truing a receiver with a lathe and there's no doubt that is a superior way to do it if you have the machine and the skills to use it.
The reason I only point out windage is that the elevation adjustment of a front sight isn't visually annoying like the rear sight is. If you have to go a little farther up or down because of the barrel, the front sight doesn't look different in the sight picture. If the rear aperture is extreme left or right, it can really grind your gears to look at even though the rifle may be zeroed just fine. You are correct that the FSB can be canted and that can be the culprit more than how the barrel sits in the receiver, but on the rifle I mentioned that was not the case.
The way I view lapping is that it's easy to do and if I have the upper taken apart anyway, might as well true it up. I wouldn't take apart an upper just to lap it unless it had the iron sight windage adjustment problem, or it had poor accuracy in general and I mainly wanted to fit the barrel to the receiver better. If I had a newer BCM receiver that my lapping tool wouldn't fit in, it wouldn't bother me as I really don't use irons much anymore unless it's a rifle getting a red dot as a primary optic.

[TWR]

Yeah it’s one of those things that doesn’t really hurt a thing if done right.

On the rifle I’m fixing to redo I noticed the anti rotation tab on the left side is against the upper while the right side has a slight gap. I install my rails with a one piece scope mount bridging the upper and rail. That way it should line the 1913 pic slots up. But this one didn’t for some reason. It is my old truck gun that I put together with extra parts and a buddy gave me the barrel. I had Daniel Defense fixed irons on it with a red dot. Never noticed the rear sight to the left but when I swapped the DD’s out for Troy folders, it’s very noticeable.

I just always assumed the rear sight to the left was because the barrel twisted a bit when torqued. But now with front sights on rails, it makes me rethink all this.