AR upper receiver lapping

[Shadow9mm]

Just bought the tool, want to give it a try. Heard it can help ensure the barrel is straight on the gun minimizing windage adjustment when zeroing, as well as increasing accuracy.

Been googling and having a hard time finding much in relation to actual testing, other than reviews which seem to be sales pitches, forum posts from people who have never done it, and one article from criterion barrels.

The article from criterion was not specific to lalping, but was more focused on the accuracy potential of their barrels. However they had data for guns before and after truing/lapping.

Here's the article. https://criterionbarrels.com/media/a...n-ar15-barrel/

Anyone done it? Thoughts?

[ocharry]

when i built my first ar build i got the lap and a reaction rod and a couple other tools to put the rifle together with plus some aeroshell 33 grease, loctite beding

i did lap the first receiver and then i built a grendel and i laped it too

when you start you will see how bad or if the nose is square....everything i read about lapping the nose said you only need min. 80% to be good....i took my recievers to about 98+...you will see when you start lapping

does it help?? well i retired from the tool&die trade and i for sure dont think it will hurt anything to have a good solid square flat seat for the barrel flange to sit on when you torque the nut down

does it help...i think it does.....the only thing i can say you should watch for is not to take anymore from the nose than you think you need and also watch the extention depth into the receiver so it does not over shoot the m4 ramp in the receiver and cause feed problems or a snag on the bullet nose ....i guess you could blend them back together but if you dont go to deep to start with you dont have to worry about that

i think the next time i think i want to do one of these rifles i want to do a thermal fit ...both of the receivers i have used had a nice ring fit to the barrel and receiver but i still used some loctite 620 on the extention to bed it even though im sure most if not all was wiped off when i sliped them together...just made me feel better

i do believe anything you do to make a good fit to parts will increase the function and accuracy of these rifles.....so if you are going to take the time to do it why not give it the extra that could make a difference

i am no expert on this...but i can tell you that i have built two rifles for myself...and worked on a couple more...ok maybe more than a couple....BUT the two that have been built from scratch by me are good shooters...i might even say excellent shooters..both will do 5/8" easy and the grendel just put down a 3/8" group...outside measured...that made me smile...i still get a grin just thinking about it

so does it help lapping the nose....i believe it does and i will always do it when i put a barrel on a receiver...why not you have the tool

ocharry

[ballardw]

https://fmgpubs.com/product/american...l-edition-pdf/

DIY Guns 2022 Volume 30 has a write up on the Wheeler AR receiver lapping with some pictures and tips, four pages. Don't know of a free version though.

[FrankenMauser]

I have lapped a handful.
For one of them, minor improvement was made.
For another, it shrank groups massively. But we're talking about massive groups. The upper was shooting 8" groups at 100 yards. After lapping the receiver, they shrank to 1.5-2.5" with the same ammo, similar environmental conditions, and the same equipment and shooter.

But they were both out of square to begin with, so a torqued barrel nut was making hard contact on one side and not much on the other.

No others showed any change attributable to lapping. Any change noted could be attributed to noise in the data.

[Scorch]

About two years ago there was a big surge in people wanting their upper lapped. There must have been an article in one of the gun rags about it. I am not sure if it helps accuracy, I have never tested it out. I have lapped maybe a dozen uppers. Better to put your money in a good barrel to get good accuracy than rely on a tool,

[Shadow9mm]

Originally Posted by Scorch

About two years ago there was a big surge in people wanting their upper lapped. There must have been an article in one of the gun rags about it. I am not sure if it helps accuracy, I have never tested it out. I have lapped maybe a dozen uppers. Better to put your money in a good barrel to get good accuracy than rely on a tool,

Or I could do both. The tool was cheap enough, about $75 for the tool and the lapping compound.

Hopefully my new barrel is good. Company said, while there are no guarantees, their expectation is 1moa or better.

Also, I have a couple uppers I will be doing. I have a couple, and at least 1 co-workers has expressed interest in doing it to theirs.

[44 AMP]

The test to see if it makes a difference seems simple. Build without lapping, shoot (doing whatever you usually do for accuracy - tuned loads, etc) then tear down the upper, lap it, reassemble and shoot, doing exactly what you did before. If there's a change in the accuracy, the lapping likely caused it.

The upper was shooting 8" groups at 100 yards.

This brought up an old memory. In the 70s, 8 MOA was the accuracy standard listed in the Army TM (forget the number) Standards for Overseas Shipment for the M16A1 rifle.

IF the rifle shot 8MOA or better, it qualified to be shipped overseas for service use. If it shot worse than 8 MOA, it was to be "retained in CONUS for training use".

I remember that number, because, at the time, it shocked me. Seemed like it was a huge number. No way I, personally would be satisfied with an 8MOA rifle!!

On the other hand, it didn't seem to matter much, the standard, I mean. I was involved in a couple of unit deployments/overseas shipments and NONE of the weaons was EVER tested to see if they met the standard or not. In fact, none was ever tested for anything, in any way.

Best I can recall, all the unit deployments I ever knew about were done basically one of two ways. Either the entire unit and all its gear was packed up and shipped, or the unit's people, personal effects and admin files and such were shipped to be "mated up" with equipment already in, or to be delivered to them, "in country".

I can't say if lapping will make a difference, I've never done it, but I've never built ARs for accuracy, when I was doing ARs for Uncle Sam, accuracy was not a concern, function was.

[stagpanther]

I used to lap my AR receivers; what I found was you can do as much damage as good if you don't control the run-out of whatever you use to turn the tool. It probably isn't worth the trouble unless you true the raceway inside the receiver as well and ensure a smooth, even lock-up of the bolt to extension. Lots of variables there. There is also the true of the handguard barrel nut to worry about. Only so many things to agonize over. If PTG made an AR blueprinting tool similar to their tools for bolt gun receivers--instead of just turning grit that mostly removes anodizing or paint--I'd consider using that.

[stagpanther]

BTW--Criterion makes excellent barrels in general, the linked article you put up appears to be an explicit endorsement of using handloads in their barrels; one of the only AR barrel manufacturers I know of that does that; most of them will tell you to go jump in a lake if you call them with problems and indicate you had used handloads.

[tangolima]

The receiver is aluminum. With anodized layer removed, it is pretty soft. The lapped area is load bearing. It transmits recoil force from the barrel to the receiver. Bedding may be a better choice, if I ever want to tinker with it.

-TL

Sent from my SM-N960U using Tapatalk

[Shadow9mm]

Originally Posted by stagpanther

I used to lap my AR receivers; what I found was you can do as much damage as good if you don't control the run-out of whatever you use to turn the tool. It probably isn't worth the trouble unless you true the raceway inside the receiver as well and ensure a smooth, even lock-up of the bolt to extension. Lots of variables there. There is also the true of the handguard barrel nut to worry about. Only so many things to agonize over. If PTG made an AR blueprinting tool similar to their tools for bolt gun receivers--instead of just turning grit that mostly removes anodizing or paint--I'd consider using that.

I was thinking about that! If the barrel nut is uneven it will still apply uneven pressure against the outer portion

[Shadow9mm]

Originally Posted by tangolima

The receiver is aluminum. With anodized layer removed, it is pretty soft. The lapped area is load bearing. It transmits recoil force from the barrel to the receiver. Bedding may be a better choice, if I ever want to tinker with it.

-TL

Sent from my SM-N960U using Tapatalk

I thought anodizing and surface coatings were for abrasion resistance and or prevention of corrosion and did not effect the over all strength of the material.

[tangolima]

Originally Posted by Shadow9mm

I thought anodizing and surface coatings were for abrasion resistance and or prevention of corrosion and did not effect the over all strength of the material.

You are right. I stand corrected. Thanks.

-TL

PS Regarding the barrel nut unevenness, I think its effects should be minor. The major concern is recoil force during the acceleration of the projectile in the bore. That force need to be transmitted to the receiver evenly, or the barrel may tilt, and hence the reason to lap. The barrel nut, other than keeping the barrel from falling out, is to crush fit the steel barrel onto the aluminum receiver. The torque may be lowered a bit after lapping. Now I am tempted to get the tool. What brand would you suggest?

Sent from my SM-N960U using Tapatalk

[ocharry]

i got my lap from Brownells

and maybe im old school or just the way i was taught but i do not use power tools when i lap

when i did my noses i did it by hand...ok may have taken a few minutes longer but i have more feel about what is hapening...and the pressure is always the same...and in this case... twist and rest get a different grip...twist and rest...always turning the part in your hand...that way you are not applying the pressure in the same line all the time

i put the lap in a V-block and put it in a vise on the mill...and i was twisting the receiver with my hand

just how i did it...im pretty sure it came out square...at least the indicator says it did

but i will say the receivers are Aero and they were not out much...but they were out....would it matter....well... square and flat is square and flat....and i know i have a good mate up with the barrel extention and the receiver nose

i will say that i didnt have to move the windage hardly at all for the scopes...so there is that too

this is just how i did it...and i do believe it helps....yep i guess you can put it together and shoot it and take it apart and lap and reassemble and shoot it again to see if it really did anything.....but you already have the barrel off and you have the lap...if you do it now you can rule that part of the equation out....when you put the lap to the face of the receiver you will know if it is square or not......i dont like doing things twice..lol...YMMV

and i also read that taking the anodize off the lap spot made it weak...i could be wrong but i call BS.....that anodize is a hard coating on the aluminum it does not make the alumnum harder or stronger...maybe a little tougher on the surface

also when the explosion happens it is trying to move the bolt and the barrel away from each other...not set the barrel back against the nose...so if there is any force being applied to the nose it is on the threads not the face...action....reaction

now i could be wrong on ALL of this but that is how i see it...YMMV and my .02 is what you paid for it

ocharry

[HiBC]

I have never machined an AR upper. I don't know the production process.

I have done some lathework. It would seem to me that a well designed fixture or setup would cut the threads and face the receiver square in one setup.

If the operations were planned around seating the barrel with stability/accuracy as a priority, it can easily be done.

There are means to use a dial indicator to inspect for runout.

I cannot say lapping your upper is unnecessary. Not all uppers are created equal. If I go with the quality level of Aero or Armalite,I believe I'll get pretty good parts. I've never built an AR that would not shoot 1 1/2 in 5 shot groups at 100 yds,just assembling parts. Maybe if I lapped I could gain some. I don't know.

On 44 AMP's 8 MOA comment: I don't doubt you know what you are talking about. Thats appalling!
IMO,its criminal to set that kind of spec. That in itself would cause me to strongly discourage ANYONE to join the military. It shows an utter disregard for the value of a Troop's life.
Wasn't the standard about 3 MOA for WW2 weapons? Even pay and advancement are tied to shooting ability. Can anyone shoot Expert with an 8 MOA rifle? What is the point of an over $1000 ACOG if you clamp it on an 8 MOA rifle?
IMO, any rifle that is not capable of delivering dependable 1 shot aimed torso (preferably head) shots at 300 meters should not be issued for combat.

I had the priviledge had shooting with a Marine at a range. I believe he was a former Captain.
I had a mongrel 16 in Hbar parts bucket gun. It had an Olympic barrel in its 3rd rifle. It would shoot 1 MOA. It had a Rock River NM 2 stage trigger. It was scoped. I think it was a Springfield.
Our Marine took a sitting position with that rifle and tore up the bull at 300 yds.
He laid that rifle across his thighs and just stared at it a long time. Then he said " If only I had something like that in combat" (Or something like that)

Its just not hard to make an AR shoot pretty well.

[ocharry]

i agree HiBC..

you would think that the set up to do the bore or bolt raceway and the nose and threads would or should be done at the same time..so everything is straight and square when it comes off the fixture

maybe it has something to do with the anodize process?? not sure..but i would think that would go on pretty evenly

not sure of the manufacturing process ... but i can tell you the nose on two aero receivers that i have was not square....would it have been ok to run with it??? im sure it would

i just like flat and square..lol anal....i did my reserch and thought ...cant hurt

ocharry

[HiBC]

Thats the foundation that the barrel rests on. It NEEDS to be flat and true!

Otherwise its like a wobbly fence post.

I don;t know. Maybe I should try it. I have a rifle with a $375 cut rifled match barrel ( few years ago) from a barrelmaker with a good rep. Its about 1 MOA,+ or -. Too good to send back but not quite what I hoped for.

I bought a V-Tor upper to reassemble it but have not torn it down. Lapping might be a solution. I don't have much to lose.

[Shadow9mm]

Quick note, I do plan to hand lap. Was not planning on chucking it up in my drill.

if the barrel nut is out, but the upper is trued, that should reduce the total error making an improvement, right?

One other thought. what is the point of reference for whether or not the face is true? is it not using the raceway as a point of reference. if one trued the raceway it would make it larger adding slop in between the upper and the tool and possible making the face less true?

[FrankenMauser]

Wasn't the standard about 3 MOA for WW2 weapons?

It was generally far more lenient, and the acceptable dispersion was typically an elliptical or rectangular pattern, rather than our common modern circular standard. Ammunition quality was taken into account for judging the rifles, by allowing quite a bit of vertical dispersion.

My friend Mike made a few videos on the subject.
Enfield No 4 vs Mauser Kar98k: https://www.youtube.com/watch?v=wZbgYrkIdhk

[ocharry]

like i said i dont know the process for doing this stuff but here is my take..lol

as far as the nut goes i would think that they are running them on a 5-6 axis lathe.. turn the o.d. punch the through hole and bore to thread dia. make the relief for the threads at the botom of the bore and face off the internal flange that mates to the barrel extention flange ...spin up a threading tool and cut the threads..then the mill head comes in and makes the flats as the chuck does the indexing and then spin up a parting tool and cut it off...everything is done at once..straight and true..proly happens faster than it took me to type this

as for the lap..the long shank goes into the raceway of the bolt...my lap fit pretty snug in that bore

one thing you need to do is oil the lap shank and the internal bore of the upper so it is slick..dont want any galling going on in there

also you want to make sure you do not get any lapping compound on the shank of the lap....slid it in there and leave a gap to apply the compound to the lapping surface..there should be a undercut there at the face of the lap surface and the shank...if you pull the lap out make sure you clean everthing off good before you re-insert the lap...you do not want any compound getting inside on the bore or on the lap shank...you will see when you put the lap into the bore of the receiver...everytime you take the lap out to check clean everything off really good...no grit on anything when you put it back into the bore

just trying to help you out here and my .02 again...

go slow... it will happen pretty quick if your receiver is pretty square to start with if not it could take a few minutes...fast is not your friend here

ocharry

[Shadow9mm]

Ok, first lapping job done. Came out fairly decent I feel. I did end up needing to use my drill. Even well lubricated the lapping bar was tight in the action. This is an aero precision upper. got 3 grits 600, 320, 220. Tried 600 and it was not quite touching the finish. 320 got the job done in 4 passes of about 10 seconds each at a slower speed. Henld the drill in 1 hand upper in the other. Figured if I put it in the vise i would end up applying uneven pressure, this way it would king of float a bit.

First Pass


Second pass


Third pass

[Shadow9mm]

and Final Pass

[FrankenMauser]

Get a good grease coating on there before torquing the nut.
It will help prevent creating a corrosion cell in the future, should water (and god forbid, salt) get in there.

[Shadow9mm]

did a quick lap on my colt upper today. was able to use the 600 grit instead of 320. cleaned up in 2 ten second passes. top lapped first and the rest followed quickly, it was very close to true.

Barrel is back on, got a new hand guard and it is a TIGHT fit. heated the rail with a heat gun and it did not want to go on. Got the upper in the fridge for a couple minutes. gonna warm up the hand guard, pull it out of the fridge, and see if i can get it together.

[MarkCO]

Originally Posted by Shadow9mm

Anyone done it? Thoughts?

When I did not know what I was doing, I did a few times. I've cleaned up a damaged receiver a time or two as well. Thoughts...waste of time and money. Only a very low quality receiver would need it, and then you are better off spending another $20 on a better receiver.

The receiver is aluminum. With anodized layer removed, it is pretty soft. The lapped area is load bearing. It transmits recoil force from the barrel to the receiver. Bedding may be a better choice, if I ever want to tinker with it.

Yes, the anodizing does create a little surface hardness. And, the portion on which the anodizing is removed is now raw aluminum. Mate that to stainless...oh no! Even on carbon steel, you will create corrosion cells that, in a little time with the thermal cycling, will create more stress risers than you eliminated making it "flat".

Best bet is buy 7075 receivers, use the proper anti-seize, and torque at the high end, 70 to 90 pounds for final. The harder extension, with proper seating by low torque with successively higher torque, will move the aluminum more than your lapping creating a rigid joint, with full corrosion protection. It is highly rare that won't get the best accuracy that the barrel is capable of. If you have a really out of spec receiver you must use, get a foil ring to use between the receiver and extension. Way better.

If you are searching for supreme accuracy, like in the 1/4 MOA range, undersized 7075 receiver or oversized extension, and thermo-fit to complete with torque in the 90 to 100 ft-lb range.

I've tested all of this with lab equipment as I was building my barrel manufacturing business up, and in consulting for other barrel manufacturers.