Beleiver in AR lapping

Ripdog28

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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.
I completely understand that which is why many companies charge far less, they know people don’t want to spend that,
 

Ripdog28

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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?
I completely understand why squaring the receiver to the bore is important. I frequently use a Mill and lathe.

As for the Bolt, 2 lugs bearing all the engagement can ensure proper lock up and ensure accuracy, Depending on what ones. But yes it will eventually fail.

I never posted in this thread to argue, only to state that most so called Mil-Spec receivers were not true to TDP. An no there are not many manufacturers that build to TDP let alone manufacturer to TDP for the commercial market. Even Colt makes separate guns for the commercial market.
 
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What does the TDP say again?

Last night it was 77* and I was just sitting on the deck listening to the waves, I had plenty of time to play. Today I should work a little so I'll get to the point. You have not read any TDP as you state above but you seem to think it means "perfect for everyone in every way" It doesn't. ARs built out here by civilians for accuracy will put a military grade rifles built to the TDP to shame. You talk about 7075 like it's unobtainium and it's the only material that will work. In the late 80s it wasn't as easy to find parts as it is now, there may have been a dozen companies to buy from. PAC WEST arms was one selling Pre-ban receivers after 94. Those were near the biggest piles of loosey goosey shit out there BUT when built correctly (squared and bedded with a button or screw to take up the slack )they can shoot 1/2MOA. I still have 2 with the original Douglas barrels chambered by Derrick Martin on them.
Anyway from all of your post you seem to think the TDP that you have not read is the key to all. it isn't. A good builder is the key to an accurate rifle. Of course the barrel has to be a good barrel but a good barrel thrown in a pile of crap is still a pile of crap. Everyone gets lucky once in a while and slaps stuff together and it comes out right but my money is on the good builder using good assembly practices for turning out consistently accurate rifles day in and day out. I like to think this forum and a few others is here to help people build or learn to build better rifles.
According to you TDP parts are the best but no civilian can buy them so why do they matter to us? You think the military using TDP parts build the finest rifles in the world and no civilian can come close? Try reading topics like this one and the books below with an open mind, there is much to learn.


I completely understand why squaring the receiver to the bore is important. I frequently use a Mill and lathe.

As for the Bolt, 2 lugs bearing all the engagement can ensure proper lock up and ensure accuracy, Depending on what ones. But yes it will eventually fail.

I never posted in this thread to argue, only to state that most so called Mil-Spec receivers were not true to TDP. An no there are not many manufacturers that build to TDP let alone manufacturer to TDP for the commercial market. Even Colt makes separate guns for the commercial market.
 
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Rocketvapor

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Well, all this is on @hitman for asking the question. Lap or no lap :)
I suggest he go post in this thread and see if all these 1/2 and 1 MOA people follow him over there :)
 
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Ripdog28

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What does the TDP say again?

Last night it was 77* and I was just sitting on the deck listening to the waves, I had plenty of time to play. Today I should work a little so I'll get to the point. You have not read any TDP as you state above but you seem to think it means "perfect for everyone in every way" It doesn't. ARs built out here by civilians for accuracy will put a military grade rifles built to the TDP to shame. You talk about 7075 like it's unobtainium and it's the only material that will work. In the late 80s it wasn't as easy to find parts as it is now, there may have been a dozen companies to buy from. PAC WEST arms was one selling Pre-ban receivers after 94. Those were near the biggest piles of loosey goosey shit out there BUT when built correctly (squared and bedded with a button or screw to take up the slack )they can shoot 1/2MOA. I still have 2 with the original Douglas barrels chambered by Derrick Martin on them.
Anyway from all of your post you seem to think the TDP that you have not read is the key to all. it isn't. A good builder is the key to an accurate rifle. Of course the barrel has to be a good barrel but a good barrel thrown in a pile of crap is still a pile of crap. Everyone gets lucky once in a while and slaps stuff together and it comes out right but my money is on the good builder using good assembly practices for turning out consistently accurate rifles day in and day out. I like to think this forum and a few others is here to help people build or learn to build better rifles.
According to you TDP parts are the best but no civilian can buy them so why do they matter to us? You think the military using TDP parts build the finest rifles in the world and no civilian can come close? Try reading topics like this one and the books below with an open mind, there is much to learn.
A lot of what you assume, I have not stated. I have not stated anything about 7075 other than it being stronger than commercially used and far cheaper 6061. Do you really think the TDP from the 60's or even 80's is still being utilized for todays guns? Clearly you are unable to read and think about what I have wrote. I will leave this thread as it is not possible to converse with people who miss state what I have wrote here.
 

Constructor

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A lot of what you assume, I have not stated. I have not stated anything about 7075 other than it being stronger than commercially used and far cheaper 6061. Do you really think the TDP from the 60's or even 80's is still being utilized for todays guns? Clearly you are unable to read and think about what I have wrote. I will leave this thread as it is not possible to converse with people who miss state what I have wrote here.
I didn't say anything about the TDP in the 70s or 80s.
You imply parts made to the TDP are perfect in every way yet you have never read a TDP.
I guess I wasn't blunt enough, I think you are FOS.

Anyone else- This is a short rundown on "mil spec" and the TDP if you haven't seen it before. Lots of testing but tolerances are still in the TDP. IMO the OP is trying to improve his rifle, pat him on the back instead of saying it wont matter it will never be as good as a milspec rifle built to the TDP. - http://www.defensereview.com/wp-content/uploads/2009/04/Combat_Tactics_The_Truth_about_MilSpec_by_David_Crane_Summer_2008.pdf
 
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Rocketvapor

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This WAS going pretty good until someone came in that didn't know how the the design gives us headspace and then the discussion on specs most of us don't care about when putting our Kitchen Built Little Black Rifles together.
It's the right to purchase sub-par inexpensive parts, apply some fitting and tuning to make long(er) range accurate sniper rifles that I'm interested in, not cherry picked (although I do some) 100 yd groups.
I've got maybe a little more than a grand, optics included in my most expensive build and it's ME that limits my accuracy at this point. Build or buy? High end or bargain? Trigger time or internet bandwidth?

and @hitman , it's i before e except after c
:)
 
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MontanaMan

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I have not stated anything about 7075 other than it being stronger than commercially used and far cheaper 6061.
I don't want to imply that you implied anything in that statement, but there's surely no shortage today of 7075 in either lowers or uppers.............they are readily available commercially to anyone not living under a rock, in fact, no serious builder would even consider anything else.

MM
 

Frankly

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Interrupting for a basic question, my newfound understanding is that the purpose of lapping the receiver and wanting a tight fit with metal shims is to remove vibration and improve consistency between shots?

I don't see how it affects the accuracy of a single shot but it could possibly tighten groups.

Even though everything is tightened down, a sloppy unsquare fit could lead to the barrel slightly wandering between shots? Have I got this right?

Has anyone actually tested and published results? I've seen posts where some dude posts a tight group to great acclaim but no before and afters.
 

Shifty6BR

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Well while you guys were yapping I went ahead and lapped a receiver that had some timing/torque grievances. I used the gg lapping tool and lapped by hand.
Here it is at about 20 turns or so
7035084

Then a just a few more...

7035088
Torqued and indexed the nsr barrel nut right up at 38ft lbs, no bn shims needed.
 

Rocketvapor

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Interrupting for a basic question, my newfound understanding is that the purpose of lapping the receiver and wanting a tight fit with metal shims is to remove vibration and improve consistency between shots?

I don't see how it affects the accuracy of a single shot but it could possibly tighten groups.

Even though everything is tightened down, a sloppy unsquare fit could lead to the barrel slightly wandering between shots? Have I got this right?

Has anyone actually tested and published results? I've seen posts where some dude posts a tight group to great acclaim but no before and afters.
@Frankly
A single shot has a group size of zero :), but if it was based off previous sight-in shots, it may end up in a different place.
(still with a really tight one shot group).
If all the barrel fitting tricks help keep the barrel in one place, transporting the rifle for that one shot may change things.
You will find anecdotal evidence on the interweb that shows improved accuracy but it's more of a better fit will 'probably' help.

The lug loading thing is also big interweb thing. You'll hear "I've never broken a bolt" (which implies bolts don't break) to broken bolts with an unknown cause "must have been bad heat treat or a handload".
Some vendors recommend it (warranty related).
Some big houses that machine their uppers from forging or from stock and assemble uppers/rifles likely don't if the work was all done in house. But, even those usually box up the uppers, sent them over to an anodizing/cerokote house, then get them back. One ding could make it unsquare.

Make your choice, $20-20minutes, might maybe probably will help the life of the rifle.

The perfect antagonist would say it is a waste of time, likely hurt accuracy and life, I never square because I buy brand x, will never break a bolt, and the extension will wear to the new bolt if I do.
 

Frankly

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Which brands do this in the course of assembling uppers? I've never seen it mentioned even by the top tier companies (JP, DD, Noveske, etc.)

It's not like I build multiple ARs per year, I'm starting to think I want to find a gunsmith who specializes in accurizing ARs if one such exists. Any come to mind?
 

jrhtx

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Any difference in the tools? Prices seem to range from about $25-$35. Some with some w/o lapping paste.
PTG is out, Wheeler, GG, Brownells, or others?
 

bfoosh006

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Just be careful with the cheaper ones. The cheaper ones may not fit as snuggly as the PTG . And a loose fit is not conducive to precise lapping.
 

Rocketvapor

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My Lapping tool shaft is 0.997" in diameter. That's 3 thousandths under an inch in diameter, 1 and a half thousandths in radius.
That 0.0015" is applied to a 7 inch length.
7035522
I use grease, takes up a little space (and Receiver Cleaner :) ).
If the grease takes up any space at all I'm looking at 0.0001" or less at the lapping surface.
Not bad for a $25 tool.

I wonder if I could degrease the tool shaft and coat it with something to take up about a thousandth in radius (0.002" in diameter?
 

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bfoosh006

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Which brands do this in the course of assembling uppers? I've never seen it mentioned even by the top tier companies (JP, DD, Noveske, etc.)

It's not like I build multiple ARs per year, I'm starting to think I want to find a gunsmith who specializes in accurizing ARs if one such exists. Any come to mind?
Surprisingly, none I am aware of.
JP might.. but who takes apart their expensive JP to check ?

I would think one of the manufacturer's would jump on it as a selling point... but that is a double edged sword.. charging 30 bucks more to "perform" the lapping ( as an option ) , will buy you the tool.

I'd love to see PSA and BCM do it.
 

Snuby642

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I would bet several of the high dollar brands of uppers have been lapped..

30$ dirty little secret shaving the group size of thier product.
Why tell the consumer for a selling point.

Next thing you know everybody will do it. Lol
 

Rocketvapor

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I read where one supplier might question a warranty return if the receiver was not square.
Bet he does it on complete uppers he sells.
"Receiver is squared and all tolerances are inspected to offer an upper that is guaranteed to shoot 1 MOA with quality ammo. "
 

2ndamendfan

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There is a shit ton of fail in this thread. Mostly involving how head space works, specifically regarding the AR platform.
 

2ndamendfan

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Not really a shit ton, just a little side tracking.
Unless you know something I don't.
Going back and double checking posts, nope you got it and understand. You are not the offender. Lapping an AR type upper receiver has no effect on headspace.
Someone either does not understand headspace AND/OR how an AR is assembled.
 
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Eoddave27

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I don’t know if high end manufacturers lap receivers but a friend of mine who is a gunsmith said it’s one of the first things he does. He has an attachment and puts the receiver in a lathe and faces it off that way. Then he uses an actual bedding compound for the barrel. I guess he worked for awhile back in the day with one of the smiths from the Army marksmanship unit and he has quite a few little tricks that really make an AR accurate. He worked over one of my rifles for me early on and the difference in accuracy was pretty amazing.
 
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mdesign

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Agree, some sorting is needed to get through the thread but some good information to be sure. Based some things shared, I started checking some parts and found that there is typically more variation in how square the face of some AR style uppers are than compared to my experience with M700 bolt receivers.

I'm surprised that this has not been identified as a gunsmithing/accuracy opportunity for the AR platform as it has been for the bolt guns. I would be interested to see the impact in accuracy and consistency if a competent machinist "trued" the receiver with a jig/fixture the way a bolt receiver is done.

The other part of this is the concentricity of the fit of the bore/chamber/barrel extension and diameter of the extension into the receiver. For a precision bolt gun, these dimensions are held within .0000.

In the end, maybe the returns are limited as many use their carbines for CQB work and minute of target is good enough but if truing a carbine gives bolt accuracy, many would consider switching.
 

Eoddave27

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Agree, some sorting is needed to get through the thread but some good information to be sure. Based some things shared, I started checking some parts and found that there is typically more variation in how square the face of some AR style uppers are than compared to my experience with M700 bolt receivers.

I'm surprised that this has not been identified as a gunsmithing/accuracy opportunity for the AR platform as it has been for the bolt guns. I would be interested to see the impact in accuracy and consistency if a competent machinist "trued" the receiver with a jig/fixture the way a bolt receiver is done.

The other part of this is the concentricity of the fit of the bore/chamber/barrel extension and diameter of the extension into the receiver. For a precision bolt gun, these dimensions are held within .0000.

In the end, maybe the returns are limited as many use their carbines for CQB work and minute of target is good enough but if truing a carbine gives bolt accuracy, many would consider switching.
I square mine in a machinist lathe. I just have an aluminum rod that goes all the way through the receiver and locks into a live center on the tail stock to stabilize it. When I first heard about facing the receiver I went through and did all my AR’s. Most were right around 1.25 MOA. After facing the receiver and using Loctite on the barrel they all dropped down to .5-.75 MOA. The facing and loctite were the only changes I made. Now as soon as I get a receiver it is the first thing I do. It really has made that much of a difference for me. I have just been using Spikes Tactical and Aero Apecision uppers though so they are not going to be built to the same standards of the higher end uppers.
 

mdesign

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I square mine in a machinist lathe. I just have an aluminum rod that goes all the way through the receiver and locks into a live center on the tail stock to stabilize it. When I first heard about facing the receiver I went through and did all my AR’s. Most were right around 1.25 MOA. After facing the receiver and using Loctite on the barrel they all dropped down to .5-.75 MOA. The facing and loctite were the only changes I made. Now as soon as I get a receiver it is the first thing I do. It really has made that much of a difference for me. I have just been using Spikes Tactical and Aero Apecision uppers though so they are not going to be built to the same standards of the higher end uppers.
Thanks, interesting. All my AR style weapons are in the SBR platform but been thinking about building an AR10 for more precision work
 

Belisarius

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I completely agree with the process!!!
Provided that the barrel extension is perfectly squared? Is that the case? Are all of them squared?
An honest question!
 

Snuby642

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Good point.

Now let us sell you a barrel extension squaring tool as well.

Lmao. It does not stop does it?
 
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Snuby642

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Question, can none of these manufacturers do thier damn job?

Seems like a lot of slackers out there.

Where has the pride went to in this day and age and why do we put up with it?
Tooling and machinery has gotten better over the years.
 

Rocketvapor

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I doubt barrel extensions are perfectly square with the barrel ID or the chamber or the bore .
Likely worse with low end mass produced barrels.
But, most of the operations are turning round steel parts.

An upper, being Anodized Aluminium Alloy :) is subject to distortion from treating after it is machined.
Indexing an upper to cut the threads and face off the front is a little more tedious with it not being a round part.
From the time the last machining operation and you building an upper my guess is the aluminum upper would have the biggest chance of being out of square.
An out of square chamber to bore don't move. An out of square extension to barrel don't move.
Slop between the upper and extension is about all the home builder can fix.

You can buy from the house that does the machining, or buy from a vendor that sells overruns, blems, and surplus.
 

Snuby642

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Anodize process does not distort aluminum. It is just a controlled corrosion process to stop corrosion basically. Done it many times by hand without heat or electrolysis. It is a tiney thin layer that eats into the metal and then has a stopping process / rinse.

As long as the parts are clean and dry and the rinse is clean it is easy, any spec of dirt or oil will show up.
 
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Rocketvapor

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If you summarize fit issues between the receiver and the extension posted in this forum you run from diameter fits that REQUIRE a thermal fit, to 1.5 thousandths shim stock (that's 3 thousandths in diameter).
That's ridiculous for modern manufacturing.
I've heard about the extension pin bottoming out in the receiver slot.
That's ridiculous for modern manufacturing.
Extension flanges that left see through gaps at the receiver.
That's ridiculous for modern manufacturing.
Sharp edges on the front of receivers from threads not being properly dressed.
That's ridiculous for modern manufacturing.

There's crap out there just waiting for someone to buy it.
 

Rocketvapor

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Snuby,
I agree that the coating/surface treatment is super thin.
Using metal polish and a lapping tool you get to see the bare aluminum pattern pop through quickly.
It's the pack and ship out process, pack and ship back, store in bins, and ship a receiver to a customer that has the biggest chance of messing up the front edge.
That is if the front edge wasn't messed up to begin with :)

A thin little ridge of aluminum at the thread start will probably compress out when torqued.
Anything more than that would likely hold you off square.
 

Yondering

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I completely agree with the process!!!
Provided that the barrel extension is perfectly squared? Is that the case? Are all of them squared?
An honest question!
A quality barrel will pretty much always have the barrel extension square, unless it's defective. With low end barrels, sometimes they are not perfectly square; I have one that way. If you get a bad one, there's not much most people can do except return it, and in most cases you wouldn't be able to tell anyway.

However - the main point of lapping is to get the barrel extension square with the receiver bore, so the bolt lugs seat evenly. A lapped upper does that regardless if the barrel extension is square to the barrel or not.

Perhaps your question was more about the barrel extension lip (which seats against the receiver) being square to the lugs - in that case, yes, even lower quality extensions are typically very square to the lugs. Both of those are part of the barrel extension, which is one piece and screwed onto the barrel.
 
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mdesign

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Good point.

Now let us sell you a barrel extension squaring tool as well.

Lmao. It does not stop does it?
Actually, I think there is a business opportunity here. I am not a machinist but look at all the shops that are "truing" bolt actions and the market options that created. Now consider all the comments on the web about the challenges of making AR10's shoot well....

Kind of wish a shop like LRI would start doing this or offering "blue printed" machined uppers. I think it would drive the market forward like the bolt action progression over the last 10 years.
 
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Snuby642

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Possibly a plastic plug with a rim for the front of the receivers and a plastic bolt for the rear.

There may be cheap turnkey products available.
What is it 1 inch in the front and if not able to match the rear exactly
A loose press in might be available.

I hated sending precision parts out of shop, come back whenever and dinged up.

I could also see using some of that thick plastic fishnet packaging , and tucked back into receiver?
 
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Constructor

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Barrel extensions are turned in 1 op, Drilled. bored, face of lugs cut, OD turned, flange cut all in one op cut off a 4-12ft rod so yes all surfaces would be parallel/perpendicular with each other. The second op only broaches the lugs and the sides of the lugs do not touch anything.

NO one these days would stick a short piece of rod in a lathe and dril one hole, throw them in a pile, pick thm up later turn the outside throw them in a pile, pick it up again face the lugs throw it in a pile etc , etc.

Any machinist with just a little common sense does all of the critical work in one op. Barrel bore is indicated and spinning true. The barrel spins while the tool is stationary. That insures the chamber, threads, shoulder for extension are all concentric on the bore and perpendicular to the bore.
 
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Rlandry

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Why does lapping the receiver face not affect head space? It seems like the barrel is being set back. Just wondering.
 

Snuby642

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The bolt will "follow" the extension in for the few thousands.

Technically I guess it would actually go back.

Bolt and extension "float in space" together.
 
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