Beleiver in AR lapping

[pugnado]

I would disagree with you based on the lengthy time I have spent in class with people who manufacturer these guns according to TDP. The dimensions are perfect if build to TDP, no lapping needed/truing of faces is needed.

MIL-C-70599 (AR)
Milspec TDP for accuracy 4.5 MOA @ 100 yards.
If you're happy with that, (and there's nothing wrong with it for killing bad guys), then don't lap or true or bother with floating handguards etc...

I think most of us here are chasing the sub-MOA dragon, so we lap our stuff, tune for this and that and spend more than $10 on a trigger, barrel etc...

 

[The King]

For those who are worried about headspace - you do not take the barre extension off the barrel.

We are discussing the act of grinding the anodized aluminum face of the receiver. In small quantity it will not result in any fault in the ar15s operation or position of the bolt carrier.

 

[Snuby642]

Does the upper need to be stripped completely to lap it?

 

[Rocketvapor]

No.

 

[pugnado]

Does the upper need to be stripped completely to lap it?

Nope, but you're gonna wanna do things to keep lapping compound where it shouldn't go, eg in the threads, between the tool and the receiver where it will make things worse not better etc... I wrap the threads with tape, oil up the shaft (hah) and check frequently that I'm only grinding the top and not inside. Afterwards, give the threads a good cleaning with a wire brush and wipe it until you see no more compound etc...

 

[Yondering]

Headspace has nothing to do with lapping the receiver. There are some goofy claims being made in this thread. pugnado, you seem to know some stuff, but you do not understand headspace and don't seem to understand receiver lapping either; please stop giving bad advice.

Headspace dimensions in an AR are contained within the bolt and barrel/extension assembly. Other than tilting the bolt at an angle relative to the extension, that is a fixed entity. Don't overcomplicate it.

 

[Ripdog28]

MIL-C-70599 (AR)
Milspec TDP for accuracy 4.5 MOA @ 100 yards.
If you're happy with that, (and there's nothing wrong with it for killing bad guys), then don't lap or true or bother with floating handguards etc...

I think most of us here are chasing the sub-MOA dragon, so we lap our stuff, tune for this and that and spend more than $10 on a trigger, barrel etc...

Do you read? Because it does not state that. Standard horizontal and vertical deviation of 3.4-4” at 600 yards is specified. Which equates to 6.8-8” group at 600 maximum. An M855 ball ammo with wind at 600 yards is incredibly accurate..

Please stop.

 

[Rocketvapor]

I guess the need/desire to lap depends on how you are using the rifle.
I shoot for accuracy, or try to. I have a rather heavy barrel, and shoot NEAR max with a 22Nosler.
Sometimes with a 5.56 bolt, and sometimes with a 6.8 bolt (Hagar brass necked down).
I desire the best alignment and stability I can get. Centering the barrel in the receiver bore and a flat and square 360 contact with the extension flange should help. My 1:7, 5R, 28" barrel doesn't seem to like 55gr bullets. The wind drift of the 80ELD @ 3000 or 88 ELD @ 2900 seems to be less than the lighter bullets.
Those that run modified bolts with a larger face and less lug support and hot loads should pay close attention to lug loading.
Once I shoot this barrel out I don't want to press the barrel out. So I won't be pressing it in.
A slight thermal fit can be tapped out with a rubber mallet.
If you are worried about headspace send a bolt to your barrel maker or buy one of theirs and specify what headspace you want.
They will run the extension onto the barrel to give you what you want. This is done before the port hole is timed (unless you ask for NO PORT ).
Work with your barrel maker.
Buy downstream from a bargain reseller or buy a cheap assembled upper and you may get a pig in a poke.
If you end up with a receiver face that you can SEE a gap at the extension flange, or slide a business card into the gap contact your receiver source.
For lapping we are talking about taking maybe one half to two thousandths off high spots to get full circle contact.
If you end up with feed ramp edges, blend them. Happens sometimes even without lapping.

 

[bfoosh006]

This sums it up quite a bit for me... 5:21 into the video

 

[clcustom1911]

MIL-C-70599 (AR)
Milspec TDP for accuracy 4.5 MOA @ 100 yards.
If you're happy with that, (and there's nothing wrong with it for killing bad guys), then don't lap or true or bother with floating handguards etc...

I think most of us here are chasing the sub-MOA dragon, so we lap our stuff, tune for this and that and spend more than $10 on a trigger, barrel etc...

That's exactly why I'm happy as a clam with my 2-2.5 MOA AR I put together.

 

[Rocketvapor]

I dread the day I put together 2-2.5 MOA AR
Actually I have one, a 10.5 inch 5.56 pistol.
It's all about that bass, I mean what you want from your build.
2 to 3 inches @ 100 kills just fine.

 

[Ripdog28]

That's exactly why I'm happy as a clam with my 2-2.5 MOA AR I put together.

To bad his information was wrong.

 

[Rocketvapor]

<<< See the avatar? I want MORE of them

 

[srt-4_uk]

Do you read? Because it does not state that. Standard horizontal and vertical deviation of 3.4-4” at 600 yards is specified. Which equates to 6.8-8” group at 600 maximum. An M855 ball ammo with wind at 600 yards is incredibly accurate..
Please stop.

That isn't what that says. It says to use ammo that is certified to that spread. Keep scrolling and it calls out rifle accuracy on page 60.

 

[CaptNemo]

I lap mine.

The group at the bottom is 5 rounds in less than 3/8” at 100 yards.
I’m not going to argue with results like this.

 

[Ripdog28]

That isn't what that says. It says to use ammo that is certified to that spread. Keep scrolling and it calls out rifle accuracy on page 60.

I’ll explain this. That target and requirements are for Iron sight test. As stated. The M855 and barrel are designed to be used together. Designed by TDP. The test I stated is the rifle fixed and used with the ammo. Not a human shooting, mechanically fixed rifle. The ammo is not required to be more accurate than the gun, they are specifically designed to be used together.

 

[Ripdog28]

I lap mine.
View attachment 7033347
View attachment 7033348
View attachment 7033349
View attachment 7033350
View attachment 7033351

The group at the bottom is 5 rounds in less than 3/8” at 100 yards.
I’m not going to argue with results like this.

Good groups but who’s upper? Is it 7075 by colt or another company with 6061. My post in this are addressing Mil-Spec sales pitches most companies use.

 

[CaptNemo]

Good groups but who’s upper? Is it 7075 by colt or another company with 6061. My post in this are addressing Mil-Spec sales pitches most companies use.

BCM. I had to turn a couple of thousandths off of the shaft to get it to fit in the carrier bore in the upper.

 

[srt-4_uk]

I’ll explain this. That target and requirements are for Iron sight test. As stated. The M855 and barrel are designed to be used together. Designed by TDP. The test I stated is the rifle fixed and used with the ammo. Not a human shooting, mechanically fixed rifle. The ammo is not required to be more accurate than the gun, they are specifically designed to be used together.

I'm not saying that isnt correct, but where is that written that it's fired from a whole weapon and not some sort of fixture? For the ammunition, it says the 600yd test is done IAW MIL-C-9963F. Then MIL-C-9963F, Para 4.4.4 says accuracy testing is done IAW SCATP-5.56mm aka MIL-C-70460. No where have I seen how its fired. They all reference the same 7.8" vertical spread at 600yds.

 

[Ripdog28]

The form i believe we are both looking at and referring to is not the actual TDP. That is owned by the US govt. companies who make the guns for them are the only ones authorized to utilize it. It is not published, ever or you will be sued by Uncle Sam. The AR15 is a close cousin but not the same.

The form we are looking at is from the US army testing. It even states Mil-Spec which is not the same as the TDP. Many things relating to the TDP not put to paper unless your the company making stuff. But i can assure you, from people who are/were making and testing military guys, what i posted earlier is Extremely close to the testing.

 

[pugnado]

I dread the day I put together 2-2.5 MOA AR
Actually I have one, a 10.5 inch 5.56 pistol.
It's all about that bass, I mean what you want from your build.
2 to 3 inches @ 100 kills just fine.

Glad I’m not the only one. My new 8.4” 300 BLK has groups like that but I’m still learning what it likes to be fed, doing ladders and data analysis as if it were a precision rifle. I don’t know why, habit, curiously. It puts holes in things, so good enough?

 

[Rocketvapor]

Groups aren't so bad from sofa to front door distances

 

[Frankly]

I appreciate this thread, tell me more!

Sure beats the Bear Pit.

 

[MontanaMan]

Headspace has nothing to do with lapping the receiver. There are some goofy claims being made in this thread. pugnado, you seem to know some stuff, but you do not understand headspace and don't seem to understand receiver lapping either; please stop giving bad advice.

Headspace dimensions in an AR are contained within the bolt and barrel/extension assembly. Other than tilting the bolt at an angle relative to the extension, that is a fixed entity. Don't overcomplicate it.

I'm glad you posted this as I was thinking the same thing; I don't think the guy has a clue.

I hope the weather is not too bad in your area, looks pretty gruesome in some, mostly south of you.

MM

 

[pilotjoe]

The best way to do it, if you can, take your barrel to the gun store and find which upper it doesn't fit in by hand. That's the one you want, bring it home....

Yep, totally agree on this. I've done 2 ARs. Both with Aero upper receivers. Both times I had to heat the upper in order to get the barrel to fit. That's the kind of fit I want.

And neither of the Aero uppers were "perfect". Both needed a little lapping. Not much, but some. Both rifles turned out great, and are real tack drivers. (At least as much as an AR can be a tack driver).

 

[Lawless]

In regards to “mil-spec”, it means built to the agreed upon standard by the cheapest bidder.

 

[Snuby642]

Having been in manufacturing to mill spec for over 30 years,
You would think built to the highest standards.

That is not necessarily the case.
Military grade, does not ensure the best available product.

They will work, and last, but you give up on precision some times.

Imho

 

[Rocketvapor]

Mil spec is fine.
The tolerances specified are producible.
Not easily, but at least with good practices and quality control.
It is, and remember this word, ADEQUATE.
Adequate enough to be reliable.
Deviate from Mil-Spec and you could have reliability issues requiring port sizing, buffer and springs, adjustable gas blocks.
Not typical Mil-Spec parts.

I like, and remember this phrase, BETTER THAN MIL-SPEC.
Tighter tolerances, different chamber, headspace, better trigger than the $10 mil spec.
Even a different cartridge spec than mil-spec.

The only way to do that is to SELECT or ADJUST.

 

[Ripdog28]

Again, Mil-spec does not mean built to TDP. The commercial market does not make a gun built to TDP. They use Mil-Spec to con people to think they have a military grade gun.

 

[MontanaMan]

There's some pretty funny shit on here............................

MM

 

[Yondering]

I'm glad you posted this as I was thinking the same thing; I don't think the guy has a clue.

I hope the weather is not too bad in your area, looks pretty gruesome in some, mostly south of you.

MM

Thanks, yeah we had some good snow but it's cleared up again now. I'm just waiting for the big snow piles to melt so I can recover the bullets I fired into them.

Since this is a thread about receiver lapping - this is the lapping tool I use. It's a Brownells reaction rod with a big nut bored and pressed onto the back end and trued in the lathe. It makes a nice dual purpose tool that way. If you already have a reaction rod, your friendly local machine shop can modify it like this pretty easily.

 

[Snuby642]

Picture?

 

[Yondering]

Hmm, you can't see it? Imgur links have worked here in the past. How about this?

 

[Rocketvapor]

I can see it if I click on the image.
Cool dual use tool.
How much did the shop charge you to bore, press, and true?

 

[Snuby642]

Nice tool. Lol

Maybe you should patent that?

 

[Rocketvapor]

A little relief cut up close to the nut would prevent any cutting action in the receiver from compound that migrated to the shaft.
Hard to tell from the picture but it might already have a relief.

 

[Yondering]

I can see it if I click on the image.
Cool dual use tool.
How much did the shop charge you to bore, press, and true?

I did the work myself - have a modest machine shop set up at home now and have been machining since the mid 90's, so I make a lot of my own gun parts (like brakes and suppressor mounts, barrels, etc) and tools. I don't know what another shop would charge; my guess is that you'd pay a 1/2 hour minimum flat rate charge. Or find the right guy and bring him some beer?

There is a shallow relief cut like you describe, to prevent abrasive acting on the inside of the receiver bore.

I don't know what's up with the pictures, sorry. They've always worked with that method before, and they show up fine for me.

 

[yej0001]

Learning here. Very informative discussion!

 

[Constructor]

I would disagree with you based on the lengthy time I have spent in class with people who manufacturer these guns according to TDP. The dimensions are perfect if build to TDP, no lapping needed/truing of faces is needed.

The TDP does not address the receiver face being out .002" across the 1" flange, there are tolerance in the TDP. If the receiver is out .002" in 1" AND the bore is not a snug fit to the barrel extension it will cant the barrel off to one side , up or down. .002" out of square relates to 9" on the target at 100 yds. In addition the bolt lugs on one side will catch all of the bolt thrust until the lugs of the barrel and extension wear or compress until the lugs on the other side touch.
IF you have to tap the barrel extension into the receiver then the bore ID and extension OD may hold the barrel straight.

 

[Ripdog28]

The TDP does not address the receiver face being out .002" across the 1" flange, there are tolerance in the TDP. If the receiver is out .002" in 1" AND the bore is not a snug fit to the barrel extension it will cant the barrel off to one side , up or down. .002" out of square relates to 9" on the target at 100 yds. In addition the bolt lugs on one side will catch all of the bolt thrust until the lugs of the barrel and extension wear or compress until the lugs on the other side touch.
IF you have to tap the barrel extension into the receiver then the bore ID and extension OD may hold the barrel straight.

I understand tolerances. The .002 is mechanical. If I take that gun and shoot a group, will it still put 10 rounds into the required max dimension? Yes it will. Every gun ever made, even full blown customs have some dimension .001-.002 off square. But that .002 does not change so
The only thing needing adjustments is the sights. However the mechanical accuracy remains the same as that .002 does not change.

The bolt lugs do not touch the the barrel extension lugs as once it is locked up, the bolt cams over and is supported by the front and back of the lugs. This still has very minimal, almost no effect on accuracy as the cartridge is supported by the chamber. The bolt only holds the case head. The Bolt and barrel extension lock up is important for function but not much accuracy. This is why blow back guns like the MP5 and Glocks are still mechanically extremely accurate.

 

[Ripdog28]

Just to clarify, I have not worked for any mfgr. I have not looked at the TDP. Like I said, only Manufacturers who have govt contracts can possess or build off the TDP, Like a patent. I have had extensive training by people who have built to TDP and who currently build them. I highly doubt any acceptable tolerance would be .002 over 1" as that is terrible. But my post above was in reference to Mechanical accuracy.

To be fair, Most receivers are just fine for the vast majority of the public. The manufacturers weigh cost vs want from their customers. 6061 alum vs 7075 is a huge price difference around 5-6x $$. Time spent on a mill is a huge cost. Spending more time, making the machine hold tighter consistencies is the difference between 1 receiver or 3-5 in the same amount of time.

If you buy a receiver build to TDP out of 7075, It will run $250+ just for a stripped upper. Big difference between that and a $40-100 upper.

 

[Constructor]

I understand tolerances. The .002 is mechanical. If I take that gun and shoot a group, will it still put 10 rounds into the required max dimension? Yes it will. Every gun ever made, even full blown customs have some dimension .001-.002 off square. But that .002 does not change so
The only thing needing adjustments is the sights. However the mechanical accuracy remains the same as that .002 does not change.

The bolt lugs do not touch the the barrel extension lugs as once it is locked up, the bolt cams over and is supported by the front and back of the lugs. This still has very minimal, almost no effect on accuracy as the cartridge is supported by the chamber. The bolt only holds the case head. The Bolt and barrel extension lock up is important for function but not much accuracy. This is why blow back guns like the MP5 and Glocks are still mechanically extremely accurate.

Assuming your requirement is only the 3MOA TDP sure anything is accurate enough for your requirements but many people have a much higher expectation of their firearm.
I've been a smith since 1980, worked as an engineer for 25 years, owned my own company making AR parts including bolts, carriers and barrels for the last 12 years.
Do you know why gunsmiths square receivers and lap bolts in bolt guns? I'm not talking about some jackleg trying to meet a 3MOA minimum that the military requires.
Do you know the bolt in an AR is the weak link? Why would you want 3-4 of the 7 lugs to bear all of the thrust?

 

[Constructor]

Just to clarify, I have not worked for any mfgr. I have not looked at the TDP. Like I said, only Manufacturers who have govt contracts can possess or build off the TDP, Like a patent. I have had extensive training by people who have built to TDP and who currently build them. I highly doubt any acceptable tolerance would be .002 over 1" as that is terrible. But my post above was in reference to Mechanical accuracy.

That tells me you have probably never checked a single receiver for square. I have been squaring receivers for highpower rifles since the late 80s. At times we ran one CNC lathe for weeks apx 2 minutes/receiver just squaring the face of receivers. It was set for touch +.002 and many times that did not clear up 80% of the face. Vltor receivers are likely the best for being square and also having a tight bore. Mega receivers had a tight bore. I have not tried every brand out there but with most you would be lucky to find 2 out of 100 that are less than .002" out across the face.

 

[Ripdog28]

That tells me you have probably never checked a single receiver for square. I have been squaring receivers for highpower rifles since the late 80s. At times we ran one CNC lathe for weeks apx 2 minutes/receiver just squaring the face of receivers. It was set for touch +.002 and many times that did not clear up 80% of the face. Vltor receivers are likely the best for being square and also having a tight bore. Mega receivers had a tight bore. I have not tried every brand out there but with most you would be lucky to find 2 out of 100 that are less than .002" out across the face.

Have you worked on commercial receivers or those built to the TDP from Colt?

You are assuming. I have an Armory on over 50 MK18, CQB commandos, M4s which I am responsible for maintaining. All built specifically to TDP. Not commercial “Mil-Spec.” I have yet to find or receive one that is not sub 1”. Several of those guns are 15+ years old and have over 40k they them and will still hold under 2”.

A bolt gun is a different animal that a Gas Inpingement gun. Tolerances on a bolt engagement will not work for a Semi/Full Auto gun. That is why I referenced a blow back gun.

 

[Constructor]

Yes I have squared Colt, LMT, CMT and DD. There are many companies that have contracts to supply parts, Colt is not the only one and "built to TDP" definitely does not mean they are the best especially when referring to accuracy.
There may be 200 different "brands" out there now most made by the same 20 companies with different names stuck on them.
I am assuming from the posts you have made. Maintaining combat rifles is not building rifles for accuracy. You seem to think every rifle is a combat rifle and minute of man is all that is needed. You say you are an armorer, at what point do you pull a barrel from service for failure to meet spec. Unserviceable, is there more than one reason, what are they?
Remember when everyone came back from Nam, they all said how bad the accuracy of M16s built to the TDP were? In the late 80s many started to figure out how accurate they could be. 3 smiths lead the way, Derrick Martin, Frank White and John Holliger. Those guys were shooting 1/2 MOA while most couldn't break 2" at 100. Those guys wrote the book on building accurate ARs. Some people call them tricks but what they did was really just good building practice.

I asked if you knew WHY smiths square receivers and lap bolts not if you knew there was a difference. Knowing we are on the Snipers hide I think you will find most here are interested in accuracy and most will do everything possible to make sure their rifles are accurate. That is why topics like this pop up. Smiths that know the "tricks" will be sought after and those that have a habit of saying "oh just slap that shit together, it doesn't matter" will be avoided like the plague.

ETA- another one you forgot to answer-

Do you know the bolt in an AR is the weak link? Why would you want 3-4 of the 7 lugs to bear all of the thrust?

 

[Rocketvapor]

I have an Armory on over 50 MK18, CQB commandos, M4s which I am responsible for maintaining. All built specifically to TDP. Not commercial “Mil-Spec.” I have yet to find or receive one that is not sub 1”. Several of those guns are 15+ years old and have over 40k they them and will still hold under 2”.

So, what do us civies do? Buy only Colt?
I don't think so.

For us unlucky home builders, Squaring receivers to get sub 1" is a fact of life.
$250+ just for a stripped upper isn't in my budget for one, much less several ARs.

Most of mine don't even LOOK like a Colt upper
But, they are 7075.

 

[Constructor]

I have yet to find or receive one that is not sub 1”. Several of those guns are 15+ years old and have over 40k they them and will still hold under 2”.

I like these 2 statements. Never seen one that wasn't sub MOA but several are 15 years old and sub 2 MOA.

 

[MontanaMan]

Ripdog28 said:


A bolt gun is a different animal that a Gas Inpingement gun.

I have an Armory on over 50 MK18, CQB commandos, M4s




Yep, sure is.

And an 18 or 20 " barreled precision AR is surely a different animal than a MK 18 CQB......................

Just sayin'.

MM

 

[MontanaMan]

Vltor receivers are likely the best for being square and also having a tight bore.

I surely agree with that on the Vltors; also the comments about Martin, White & Holliger.............maybe add Paul Craddock to that list today, but he spent a lot of time with Holliger, too.

MM

 

[Ripdog28]

I like these 2 statements. Never seen one that wasn't sub MOA but several are 15 years old and sub 2 MOA.

Incase you miss Understand sub 1” fresh barrels and guns. Colt barrels still after 15 years of use still under 2”.