Facing AR-15 receiver

[supercorndogs]

I have heard of tools for this purpose, but I have never seen one so I am to sure how they work. I assume most of them go into the receiver where the barrel extension goes in an attempt to force the tool to cut the face square with the receiver. It seems to me considering the tolerances involved to make the tool fit in even most receivers it is only going to be able to cut semi square to the receiver.

When I worked in the shop and we needed to flatten out a surface we would use a piece of sand paper on glass. Anybody ever try to face receivers this way besides me?

 

[PappyM3]

I have heard of tools for this purpose, but I have never seen one so I am to sure how they work. I assume most of them go into the receiver where the barrel extension goes in an attempt to force the tool to cut the face square with the receiver. It seems to me considering the tolerances involved to make the tool fit in even most receivers it is only going to be able to cut semi square to the receiver.

When I worked in the shop and we needed to flatten out a surface we would use a piece of sand paper on glass. Anybody ever try to face receivers this way besides me?

The sandpaper on glass would level the front of the receiver, but it wouldn’t necessarily square it to the action.

This is the lapping tool. It doesn’t work with thermal fit receivers, but it is a tight enough fit with normal receivers that it will most likely improve the straightness of the receiver face and make it more squared off. The times when it won’t, the receiver’s face is already squared off enough.

 

[CoryT]

The question really is what are we trying to accomplish. Do we want the face square to the threads or the extension hole? If the extension fits the receiver as a proper press fit, coupled with locking compound, does the face bearing surface even matter? Shim the extension to press fit, use Black Max and who cares if the face is perfect, it pretty much cannot affect anything.

 

[Charger442]

The question really is what are we trying to accomplish. Do we want the face square to the threads or the extension hole? If the extension fits the receiver as a proper press fit, coupled with locking compound, does the face bearing surface even matter? Shim the extension to press fit, use Black Max and who cares if the face is perfect, it pretty much cannot affect anything.

Finally!! Thank you!

This has been a topic for a couple years now and all I can think is "why?"

 

[supercorndogs]

The question really is what are we trying to accomplish. Do we want the face square to the threads or the extension hole? If the extension fits the receiver as a proper press fit, coupled with locking compound, does the face bearing surface even matter? Shim the extension to press fit, use Black Max and who cares if the face is perfect, it pretty much cannot affect anything.

This is the first one i have touched with anything. It took about 30 seconds to clean it up. What I was trying to accomplish was even contact and a stress free union between the barrel extension and receiver face.

While I was doing so I was thinking, even if the does make the face contact the barrel extension more evenly. What about the lip on the barrel extension. Is it flat? What about the nut where it contacts the other side of the barrel extension. Is it flat. What about the distortion from tightening the barrel nut? How far out would it have to be before the nut couldn't force the barrel exertion into even contact? But also how does that stress effect things? While also wondering if it mattered at all.

I wouldn't call "press fit" proper fit. Press fit is a boutique fit. The face can effect some things like where your barrel points. I would be more concerned about the face being square if I had a press fit receiver personally. If its press fit and the face is out of square, that stress is going to be transferred to the barrel extension and receiver. Not that its not debatable that it doesnt matter.

I just glue barrels with some 609 loctite normally. Before that I put together some good shooting ARs doing nothing.

 

[346ci]

I bought one of the lapping tools to do this and when it arrived I knew there was nothing precise about it.

If I'm not using a Mega or Vltor upper, it gets sent to Lee Wells for the lathe. https://accurateandreliablerifle.com/

 

[Constructor]

The question really is what are we trying to accomplish. Do we want the face square to the threads or the extension hole? If the extension fits the receiver as a proper press fit, coupled with locking compound, does the face bearing surface even matter? Shim the extension to press fit, use Black Max and who cares if the face is perfect, it pretty much cannot affect anything.

Shimming is not a good idea unless you can wrap the shim all of the way around the extension. As well as squaring the front face the idea is to create a rigid connection. If the shim is only 1/4 way around then 2 sides aren't touching the ID of the receiver.
If it is a press fit without shimming you do not need to square the face because it will be held square by the ID/bore of the receiver. If the fit is loose squaring the face will make the lugs in the extension square with the receiver along with keeping the muzzle pointed inline with the bore of the receiver.
We have been squaring receivers and using blue loctite since the 80s, it must work or all the highpower guys wouldn't do it.

 

[bfoosh006]

FWIW, and in my experience, ...

Pacific Tool and Gauge Lapping tools fit standard / non-thermal fit uppers great. Both AR15 and Large Frame ( granted two different sized tools. )

The Brownells AR15 one fits Thermal Fit uppers best.

The cheap / crappy Wheeler one, is such a loose / wobbly fit, you might ( probably ) do more harm than good... the Wheeler one now spends its life burnishing the insides of buffer tubes.

The most positive results seem to be more consistent group sizes, with less flyers. BUT, I Loctite the RE into the upper, and prefer a snug upper to lower fit. So, YMMV

Lapping the upper is so easy, I do it to all the uppers I assemble.

Does it matter in a combat AR ? that depends on you, I prefer any easy precision enhancement I can get.

 

[The King]

Here is the question for the IDGAF crowd - is the clamping force from the barrel nut enough to get the barrel extension to move if that face isn't flat. I'm betting on yes, just because the upper is aluminum.

 

[CoryT]

Here is the question for the IDGAF crowd - is the clamping force from the barrel nut enough to get the barrel extension to move if that face isn't flat. I'm betting on yes, just because the upper is aluminum.

Depends on the extension fit. With a full wrap shim, or a cut to size for a press fit, the nut is not going to cant the barrel in the receiver.

 

[The King]

Depends on the extension fit. With a full wrap shim, or a cut to size for a press fit, the nut is not going to cant the barrel in the receiver.

Makes sense.

I lap and press fit or shim fully. Seems to work good.

 

[redneckbmxer24]

Ask yourself this… do you really think that a $50 lapping tool is going to make the receiver as square as a $500K CNC?

Buy a high quality receiver like a VLTOR MUR and then bed the extension with loctite 620.

 

[supercorndogs]

That got me looking and the 609 I have been using is only meant for gaps up to .005 and press fits.

 

[bfoosh006]

Ask yourself this… do you really think that a $50 lapping tool is going to make the receiver as square as a $500K CNC?

Buy a high quality receiver like a VLTOR MUR and then bed the extension with loctite 620.

While the CNC machine is precise... in my experience the anodizing tends to be the culprit.

I have seen a lot of variance in anodizing thickness.

 

[Constructor]

Ask yourself this… do you really think that a $50 lapping tool is going to make the receiver as square as a $500K CNC?

Buy a high quality receiver like a VLTOR MUR and then bed the extension with loctite 620.

Yes. Most CNCs don't cost $500,000 mine were around 120,00each, you don't need a huge mill to cut receivers a twin pallet system runs around 250 and that is a big machine. Upper receivers are machined on a pallet system with 4 bolted to each side meaning 16 are machined at a time on not always on the same axis. The pallet system has play in it, it just held in place by clamps. Also when you buy a new CNC the company techs come out to run a test to make sure the machine is within specs. Those guys will tell you right off temperature in the shop makes a difference, temperature of the material changes and can effect the end product. The point is they are machined on a pallet system in a Mill the receiver is never checked in a lathe spun upon the bore.
IF the receiver was being spun upon the carrier bore and a tool was held stationary like we do on a lathe then I would say the face would be square. I mean that is the way I square them but most people don't have a big lathe capable of doing that so a little tool run by a drill is the next best thing because the tool is spinning upon the bore and as long as the face of the tool is square to the shaft it will work.
I've faced 10s of thousands of receivers over the last 30 years and almost all of them are .002 off across the face.
Vltor and Mega were the first 2 brands maybe 20 years ago that had a small bore where the extension needed to be tapped into place. Now other companies that have figured it out and have started offering and advertising thermofit or whatever they call it receivers. Those don't need to be squared because they are held square by the ID of the bore and OD of the extension.
ETA- If all of that receiver squaring is to get better accuracy off a bench rest, running cheap barrels, 6lb triggers, red dot sights or running and gunning then squaring the receiver probably wont help your accuracy much, it may help distribute the thrust evenly on all bolt lugs.

 

[supercorndogs]

The only "glued-in, high-quality, cut-rifled barrel in a VLTOR MUR upper" I've had, shot the least good out of my precision ARs. I'm in the "it's all internet lore and Vudu" crowd.

@Ledzep posted something the other day about shooting some groups then gluing the barrel in and seeing a fairly significant improvement in groups at 200y I believe it was. I have some pretty good shooting up uppers I glued the barrel in on, but looking at the information on the 609 I have been using. I am not sure its doing much if the clearance is over .005. I think the 620 mentioned might be a better choice. I am not sure what the clearance is between the extension and receiver but .005 is a pretty small measurement.

 

[Constructor]

@Ledzep posted something the other day about shooting some groups then gluing the barrel in and seeing a fairly significant improvement in groups at 200y I believe it was. I have some pretty good shooting up uppers I glued the barrel in on, but looking at the information on the 609 I have been using. I am not sure its doing much if the clearance is over .005. I think the 620 mentioned might be a better choice. I am not sure what the clearance is between the extension and receiver but .005 is a pretty tight gap.

A piece of copy paper is usually .004" thick. You really should not be able to get a piece of that between your extension and receiver bore, not even a little piece.

 

[supercorndogs]

A piece of copy paper is usually .004" thick. You really should not be able to get a piece of that between your extension and receiver bore, not even a little piece.

If I could rap paper around it and just barely slide it in there, that would leave potential for .008 gap correct? I.E The barrel extension sits on the bottom of the reviver I.D leaving effective 0 gap and top gap would be .008?

 

[supercorndogs]

Maybe I'll give 620 a try and see what improvement occurs.

I was just looking at spec sheets and 620 is good for wider gaps. 609 and 620 or both retaining compound for cylindrical objects. I am not saying I have ever seen an improvement from gluing. When my barrels gets here tomorrow I can try to see what kind of gap I have.

 

[Constructor]

If I could rap paper around it and just barely slide it in there, that would leave potential for .008 gap correct? I.E The barrel extension sits on the bottom of the reviver I.D leaving effective 0 gap and top gap would be .008?

Yes, but I hope you can't do that. That is a huge gap and I would start measuring the extension and bore of the receiver to find out why.
OD should be .998-.9987" Id of the receiver when machined before anodizing should be 1.00" but I can't find the drawing with the tolerance spec at the moment.

 

[supercorndogs]

I just tried to slide the old barrel into the receiver with a 1/4" wide piece of paper shimming one side of the extension and it would not slide in all the way. Thanks you saved me 30 dollars purchasing different Loctite.

 

[The King]

the other thing thats VERY true is shimming, gluing, lapping, smacking, tapping, rapping, happing....isn't going to do shit to make a POS barrel shoot.

 

[Constructor]

the other thing thats VERY true is shimming, gluing, lapping, smacking, tapping, rapping, happing....isn't going to do shit to make a POS barrel shoot.

If I was running carbine courses and 3 gun shorts then no I probably wouldn't be concerned with it because position, heart rate breathing and everything else will affect the accuracy more. I do it for long range and on rifles I use to work up loads. This was a bad group (my problem using a bad aiming point and yanking the first shot) working up a load for a TAC6 "self defense" load. Using a Dillon if I can get them down to 3/4 MOA I let it go and start loading. Yes that piece of out of level duct tape was the aiming point.

 

[The King]

If I was running carbine courses and 3 gun shorts then no I probably wouldn't be concerned with it because position, heart rate breathing and everything else will affect the accuracy more. I do it for long range and on rifles I use to work up loads. This was a bad group (my problem using a bad aiming point and yanking the first shot) working up a load for a TAC6 "self defense" load. Using a Dillon if I can get them down to 3/4 MOA I let it go and start loading. Yes that piece of out of level duct tape was the aiming point.

Yeah - me too. I'm all about the accuracy.

 

[The King]

I was just thinking the same thing. I wasn't going to bother posting it because it doesn't further the discussion of how to true a receiver but I think we all agree that accuracy is in the barrel, the ammo, and the shooter. Researching online and fine tuning one small facet of the rifle probably provides the smallest degree of improvement. When you think about the ammo that people actually shoot. Not the one-off boutique stuff that they spend a bunch of money on so they can shoot groups and post on the internet but the stuff that they reach for on any given day or buy in bulk....along with the shooting conditions that most people shoot in within their discipline of long range precision AR and how well they're really executing shots... if truing a receiver and gluing it in has some small increment of improvement we're probably not loading or shooting inside of that

The only testing I have seen shows that if you have a flopper of a barrel fit, green loctite and shims and facing helped a good bit. I also feel but don't know know that having it be perfectly straight cuts down on bolt breakage.

 

[PappyM3]

Well. I have a barrel that shoots pretty good and I put it in a sloppy Aero upper and it shot about the same. I am going to loctite it and see how much it improves. Maybe I'll get real crazy and take it to my buddy/ smith and have him true the face first.

Joe Carlos says he has seen about 1/3 taken off group size when shimming a barrel extension (or replacing the barrel extension with a tighter fitting one) and using green loctite.

I wouldn’t be surprised by a 10-15% improvement in group size by just using green loctite by itself. I’d be curious about actual results of your test though.

 

[Constructor]

Well. I have a barrel that shoots pretty good and I put it in a sloppy Aero upper and it shot about the same. I am going to loctite it and see how much it improves. Maybe I'll get real crazy and take it to my buddy/ smith and have him true the face first.

If I'm building a rifle for accuracy then I'll spend a little extra time and do what I can to try to get the best out of it. If I'm building uppers to sell, I do it every time.
That load in the photo and rifle combination above is probably a 1/4MOA load but I'm not a 1/4MOA shooter most of the time. It has taken almost 2 months to get it to that point trying 3 different primer types with 7 different powders with the 90gr Lapua alone at 5 or 6 different load lengths. That is roughly 100 combinations. I tried the 95SMks first and got close then opened a new box to find out Sierra is now pointing the bullets making them too long to load at mag length and get to the sweet spot. The ELD-X bullet tips were deforming during seating so I had to stop trying those. I like shooting but it gets old trying different combos after a while.
5.56s are a different story, at the distances they shoot 3 gun around here 3 MOA would be plenty good enough to win the match. Just about any surplus will do that including Wolf. IMI Razor core probably works better than any surplus and Black Hills 69 and 77 is probably the best factory loaded ammo that I have tried in what I shoot.

 

[MustangGreg66]

For you guys gluing in the barrel to the receiver. When the barrel is shot out, are you trashing the upper receiver along with the barrel?

 

[Constructor]

For you guys gluing in the barrel to the receiver. When the barrel is shot out, are you trashing the upper receiver along with the barrel?

We have always used blue loctite, then we just tap the barrel out of the receiver with a wood dowel/broom stick.

 

[PappyM3]

For you guys gluing in the barrel to the receiver. When the barrel is shot out, are you trashing the upper receiver along with the barrel?

Nope. If need be, just use a wooden dowel and a hammer to knock out the barrel. Then you can clean up the 609/620 loctite remnants.

 

[Rocketvapor]

My Wheeler lapping tool is about 0.003" below 1.000".
BUT, thats about 6" from the lapping rim. That's not much of an angle.
I use grease on the tool to take up a little space.
The receiver is held vertical in a padded vice and only the weight of the tool, turned back and forth, lifted and turned some more by HAND. Like hand lapping valves in a cylinder head

I use the BCA side charging upper for my prone rifles and lap for a nice even contact.
I think the goal of lapping is to align the extension/barrel with the receive bore, not receiver threads with the barrel.
Although probably pretty close to the same thing, maybe.

Now, my little deviation from shims or glue.
Since the OD/ID difference is usually only one or two thou, I mask and spray high heat rattle can paint on the extension, Just enough to fully cover the metal, 0.002" or so. Let it cure, check with micrometer, then burnish with 800-1000 grit paper.
With a thin coating it would be really hard to NOT get it equal all the way around so the extension will be centered in the receiver.
The goal is for an interference fit that requires placing the barrel in the freezer and the receiver in the oven until too hot to handle (temperature difference of at least 200F)

Put it together with a hand tightened barrel nut and let temperatures settle. The compressive strength of automotive paint might surprise you

If I was really worried about the tool angle in the receiver I could probably even use the spray on shim to bring it up to about 0.999" or so.
A one thou coating would do it.
Oh hell, why not. Might work Degreased and coated. I'll cook it, polish and Mic it in a day or so.

Sprayed a second time to add just a little more. Cure, polish and measure again.

 

[Blackcreek]

What about using a tapered or expanding mandrel and facing it on a lathe between centers?

 

[papershredder]

What about using a tapered or expanding mandrel and facing it on a lathe between centers?

The mandrel can go right in a chuck, use an indicator to dial in the mandrel. If I had a lathe, that's what I'd do, since I don't:

Couple questions for everyone since I'll be travelling down this road soon enough. Anyone know of a source for .0005" or .001" shim stock that is not plastic? Or for that matter know of anybody who will make a custom extension for a large frame AR? My current extension is about a thou and a half smaller than receiver, would rather have a resistance fit.

 

[wade2big]

For you guys gluing in the barrel to the receiver. When the barrel is shot out, are you trashing the upper receiver along with the barrel?

A propane torch on the upper for a few seconds will expand the aluminum enough that the barrel can easily be removed.

 

[srt-4_uk]

For you guys gluing in the barrel to the receiver. When the barrel is shot out, are you trashing the upper receiver along with the barrel?

Along with what other have said, a mallet and a reaction rod makes quick work of it too.

 

[ron_c]

FWIW, and in my experience, ...

Pacific Tool and Gauge Lapping tools fit standard / non-thermal fit uppers great. Both AR15 and Large Frame ( granted two different sized tools. )

The Brownells AR15 one fits Thermal Fit uppers best.

The cheap / crappy Wheeler one, is such a loose / wobbly fit, you might ( probably ) do more harm than good... the Wheeler one now spends its life burnishing the insides of buffer tubes.

The most positive results seem to be more consistent group sizes, with less flyers. BUT, I Loctite the RE into the upper, and prefer a snug upper to lower fit. So, YMMV

Lapping the upper is so easy, I do it to all the uppers I assemble.

Does it matter in a combat AR ? that depends on you, I prefer any easy precision enhancement I can get.

Apparently large frame AR's vary some in the barrel to receiver bore. I purchased an AR-10 Upper Receiver Lapping Tool from Pacific Tool and Gauge Tool that would not even start on an Armalite AR10A receiver. Measuring both the tool and the bore of the receiver, they were the same diameter at 1.187. It would go into the back end of the receiver where the BCG goes. I called PTG to see what I should do about the lapping tool. I was told someone would call me back but alas, I haven't received a call back.

Not wanting to send the tool back, I removed enough material so it would finally slip in with a snug fit but still rotate easily. It took a little time to remove the necessary material for the tool to work as it should ,with my receiver.

​

 

[JohnCarter17]

Ask yourself this… do you really think that a $50 lapping tool is going to make the receiver as square as a $500K CNC?

No, because it's a stupid question. It's a pathetic appeal to authority.

There are known tolerance issues in the manufacturing of ARs. The cost of the machine is irrelevant. The quality of the input elements, condition of the machine and proper usage by its operator(s) are relevant.

Said $500K machine isn't the only tool utilized in every step of producing a finished upper from stock.

 

[JohnCarter17]

I have had success with the Brownells tool on my thermal type (BCM, Noveske) uppers. It's a minor amount of extra work to possibly increase accuracy. I have seen various amounts of anodizing removed in the truing process, but never the entire face. Most of the time it's a little bit of metal exposed.

I do it with the upper oriented vertically, face on top, so the tool is dropped in from above and hand rotated 6-12 times each direction. So just it's mass is doing the work. Using a drill or power tool is just risking taking too much off.

I have been satisfied with the results, but we are talking about with Lilja(3), White Oak(1) and Faxon(1) barrels. Rosco next.

 

[rpoL98]

 

[ron_c]

Were these done with lapping tools or on the lathe?

 

[rpoL98]

lapping tool: PTG for the AR-10, Brownells or PTG on the AR-15's, looking for the snuggest fit to the receiver bore. certainly not the Wheeler POS (JMHO). X-Caliber for the M5E1 Enhanced. I use a cordless drill motor. I'll do a session, do 3-5 in a row, saves on set-up, clean-up time. it's a messy operation, lots of paper towels, Q-tips, for current & planned projects.

 

[Molon]

Anyone know of a source for .0005" or .001" shim stock that is not plastic?

...

 

[ron_c]

rpoL98​

Did you have any problems with the PTG Tool not going in the Large Frame receivers?

 

[rpoL98]

Were these done with lapping tools or on the lathe?

Did you have any problems with the PTG Tool not going in the Large Frame receivers?

nope, never had that problem. but then again, I only have Aero M5 upper receivers. snug fit. wheel bearing grease.

I get SS shim stock from McMaster-Carr.

 

[papershredder]

...

Thanks!

 

[Obi-WanKannoli]

To me, if your goal is to build a precision gas gun... spend a little more and just buy a receiver set from the factory that is square.

That said, if a gun has been painted or cerakoted over the barrel nut threads then yes I would definitely lap it square. I have done Lapped a reciever for this reason.

 

[ron_c]

Out of curiosity, has anyone or know of a source, where the receiver in mounted in jig that allows the receiver to rotate about the BCG bore and measure the runout on the face. Remove it, use a lapping tool, remount the receive in the rotating jig, then check what the runout is afterwards?

 

[PappyM3]

To me, if your goal is to build a precision gas gun... spend a little more and just buy a receiver set from the factory that is square.

That said, if a gun has been painted or cerakoted over the barrel nut threads then yes I would definitely lap it square. I have done Lapped a reciever for this reason.

Do you have a store where you can parooze through uppers with squares and/or other measurement tools? And then you just buy the best?

Because I can assure you even good quality and spendier uppers can have enough variation in anodizing thickness that it is worth lapping for a precision build.

 

[Constructor]

To me, if your goal is to build a precision gas gun... spend a little more and just buy a receiver set from the factory that is square.

That said, if a gun has been painted or cerakoted over the barrel nut threads then yes I would definitely lap it square. I have done Lapped a reciever for this reason.

They will all say they are all square but they aren't, you are better off buying the ones known to be tight.

 

[bfoosh006]

...

Graingers ?