Any AR builders/tuners — Lapping Q?

[Rsadams]

I have been building ARs for awhile now or should I say assembly.... Not really that hard but recently I have started trying to get the absolute most accuracy I can from one I built a few years back.... Just boredom at its finest while I wait for either good or bad news from the doctors....

My question is do you lap the upper receiver to barrel to square them up..?? It's probably the only tool I don't own , I am sure there's something else but after working in a family owned machine shop for years I was going to order one and do it , once again boredom .... Do you think it's worth it..??? This is still a non free floated barrel non chrome lined with an a frame front sight but I think putting a good barrel and free float with a adjustable gas block when this barrel is done since it's a scoped rifle...

 

[msalm]

If you have access to a lathe, turn a mandrill that you can slide through the upper with a center on one end. Slide the snug mandrill through the upper from rear to front, support with live center at front of receiver. A parallel machinist clamp will bind the receiver to the mandrill and just take a light facing cut with a sharp carbide tool…done in less time it took to type this reply…and yes, it does help along with lock tight on the barrel extension/upper joint.

 

[Walt Krafft]

IMO, don't waste your time and money. The bolt is basically free floating, and the front face is not going to be much out of square. Lots of things will make a difference, this is not one of them.

 

[Rsadams]

If you have access to a lathe, turn a mandrill that you can slide through the upper with a center on one end. Slide the snug mandrill through the upper from rear to front, support with live center at front of receiver. A parallel machinist clamp will bind the receiver to the mandrill and just take a light facing cut with a sharp carbide tool…done in less time it took to type this reply…and yes, it does help along with lock tight on the barrel extension/upper joint.

Nice , unfortunately when my father died a couple of years ago we sold our shop outright lock stock and barrel... I have moved since then and don't have access to machines anymore.... I was just going to buy the tool and hand lap it... Seems like it would help...

 

[Rsadams]

IMO, don't waste your time and money. The bolt is basically free floating, and the front face is not going to be much out of square. Lots of things will make a difference, this is not one of them.

I may be not understanding... lol wouldn't be the first time.... I adjusted my OP , what I mean is the front face of the upper receiver so the barrel fits into it square and isn't pointing one direction or another instead of perfectly straight...Is this what you also talking about not the bolt face itself...

 

[Walt Krafft]

I have never seen one so out of square the barrel was pointing so it couldnt be zeroed. If the front face was out of square for that to happen, would you square it to the bore or the top rail? Why assume the top is in alignment to the bore?

 

[gunsandgunsmithing]

Not sure how much it helps but I have a fixture that allows me to true the front of the upper square and perpendicular to the upper, where the bbl extension goes in. Simple 1" rod that lets me put the upper on it and machine it between centers. Works well. Some are out quite a bit, fwiw.

 

[LVLAaron]

My two cents based on the 8-9 I've done.

Lapping and bedding the barrel into the upper will ABSOLUTELY make a noticeable difference. For 9/10 AR's I would not bother. If you are building a target rifle, it's a must. I'd go as far as to say it's a 1/4 MOA improvement.

 

[akajun]

I’ll be the lone dissenter
Check it, 99.99% are fine, but I did have one , there was a burr or high spot next to the notch for the barrel extension pin, about .007 iirc
Would not let the barrel shoulder and nut tighten up right.
Simply dressing it up with a file then I made a lap out of a piece of scrap and ground the face with valve compound. Shot great after
So would I buy one? Prob not. I would check the flatness of the upper face against a known flat surface.

 

[jkohler]

barrel extension to upper fit seem to make a bigger difference than about anything. When I was playing with them I used to order oversized extensions from BAT so they were a press fit to the upper when I was chambering barrels for them. You can also use some .001 to .0015 shim stock depending on the upper size to tighten that fit up. A heat gun will help get it all to slide together.

 

[msalm]

Knights Armament ended up bedding the extensions onto the receivers of the M110’s (308/7.62) rifles. This was one thing that enabled them to meet the accuracy requirements for the contract. Not sure the compound used, but it definitely permanently affixed those barrels to the upper!

 

[msalm]

IMO, don't waste your time and money. The bolt is basically free floating, and the front face is not going to be much out of square. Lots of things will make a difference, this is not one of them.

It’s not the squareness to the bolt this fixes, it prevents shifting of the barrel in the upper between shots. Most are out of square by a thousand or more, and are not flat by any means. As mentioned by another poster, the Bat extensions were the best also. After threading/chambering through the headstock and checking runout, with the extension installed they didn’t runout more than a thousandth. Some other OEM extensions I saw up to 15 thou runout. The more you can unify that junction between the barrel and receiver, the more accuracy potential you will have IMO.

 

[Walt Krafft]

You fix the barrel to the upper so it doesnt move with bedding of some kind. I used blue locktite.

 

[jelenko]

Disclaimer: I have not stayed at a Holiday Inn.

I have lapped all my uppers and bed the barrel extensions into the receiver with a low strength loctite.

I have not tested to see if there is a difference.

I'm going on the theory that it can't hurt and enough people who shoot small groups with AR say they do it/it helps.

ETA. I would also modify the upper/lower to reduce bolt tilt if it were easy to do - but it isn't. And, it isn't needed to shoot 1/2 MOA groups.

 

[Rsadams]

When this barrel is shot out I will replace it with a decent barrel and buy the tool to hand lap the front of the receiver so it's true and install a free float handguard with an adjustable gas block.... it's a new build and I have only tested to loads I have been working on for it...I installed a decent scope and decided to try one of the Magpul bipods and a few other things I don't normally run on an M4... I am just board right now waiting on some medical news and thought I bet I can make this shorty shoot... Then I started looking into the things people do to make an AR accurate that I wouldn't normally do on a defensive fighting rifle... Normally as long as the rifle functions flawless i am happy with it... I do expect it to shoot MOAish off a benchrest but then found out you can get these things to shoot well.... I am just using this one to test and see what all you can do and once that's figured out will probably build a decent 20inch full size for accuracy when I get the time...Seems like it would be fun of course I said that about alot of things in my life...lol At least I will learn something new and just enjoy tinkering with the AR platform....

 

[Rsadams]

Disclaimer: I have not stayed at a Holiday Inn.

I have lapped all my uppers and bed the barrel extensions into the receiver with a low strength loctite.

I have not tested to see if there is a difference.

I'm going on the theory that it can't hurt and enough people who shoot small groups with AR say they do it/it helps.

ETA. I would also modify the upper/lower to reduce bolt tilt if it were easy to do - but it isn't. And, it isn't needed to shoot 1/2 MOA groups.

I would like to be able to remove the barrel without getting the torch out and do understand the difference in locktite IE red , blue , green and purple... I use the purple for alot of things and like it because you can get it apart again easily.... when you say low strength locktite what do you mean....

 

[pdhntr]

I have been building ARs for awhile now or should I say assembly.... Not really that hard but recently I have started trying to get the absolute most accuracy I can from one I built a few years back.... Just boredom at its finest while I wait for either good or bad news from the doctors....

My question is do you lap the upper receiver to barrel to square them up..?? It's probably the only tool I don't own , I am sure there's something else but after working in a family owned machine shop for years I was going to order one and do it , once again boredom .... Do you think it's worth it..??? This is still a non free floated barrel non chrome lined with an a frame front sight but I think putting a good barrel and free float with a adjustable gas block when this barrel is done since it's a scoped rifle...

I got one from the manufacturer that didn't seem to show any high spots at all when used the first time. I thought the upper was just fine at that point. Something just didn't seem right.

I chucked the tool up in my lathe and found the face that is supposed to "square" the receiver was off .015! So if you are going to buy a tool, I would get it checked before using.

Jim

 

[jkohler]

620 I believe is what was used quite often. It needs somewhere in the 400 degree range. Even the shim stock method requires some heat to separate them.

 

[Rsadams]

Awesome thanks for the input everyone.... I think I may have opened myself a can of worms...lol

 

[Konocti's Wigwam]

I've lapped rings in the past using a manually turned section of 420 stainless. The only reason I used this stock was that I had it on hand. I just used a grooving tool to slot grooves and used diamond paste to lap with. I used stainless as I wanted a crisp contact point for the diamond paste. I pretty much copied the wheeler kit. Midway has it, check pics out.

Wheeler Scope Ring Alignment Lapping Kit 34mm

This kit improves scope mounting two ways. First, the short bars let you know when the front ring is in perfect alignment with the rear one. Second,...

www.midwayusa.com