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Discussion Starter · #1 ·
Until I came here, I had never considered the interface between barrel and reciever to be anything but "true & square".
Well sir, I've ordered a tool to square my reciever.

QUESTION:
Am I looking to remove just enough material to give the barrel a square seat? i.e. different widths?
Or am I looking for a consistent width face all the way around the reciever?

Is it ok to chuck the tool up in my variable speed drill?
High speed?
Slow speed?
No pressure?
Little pressure?
A lot of pressure?

Will the tool need to be occasionally trued/squared?
 

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I use a cordless drill on low speed with minimal pressure. I like to get a nice even ring on the complete face. May not be necessary but it doesn't take much off.
 

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I used my cordless drill, with the lapping compound. Worked like a champ. I definitely cant complain about the results.
 

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I never considered an issue but noticed my last build is about 4 MOA off windage at 100 with a Larue mount which is usually pretty close on windage.
I shall try this squaring of the barrel extension “seat” or barrel nut connection point.
 

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Discussion Starter · #6 ·
I've built several AR's, never even considered that the barrel extension and barrel mounting ring might not be "quite" square....but it makes sense!
I watched several on YouTube.
Most preferred a relatively even ring. A couple guys weren't concerned with even, just a smooth, clean edge all the way around.

Tanlover442
Very correct, you can always take a little more off. Putting it back can be a real bear! LOL!
 

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I've been using the PTG upper lapping tool (in both small-frame and large-frame varieties) for years. I always lap them until I get an even, consistent ring all the way around. IMO, that's the only way to ensure you have equal and even pressure all the way around the barrel extension collar.

That's not to say anyone else's method is wrong (or that mine's right...), but that's the way I justify to myself the sheer amount of time it takes to get some receivers to that point. :LOL: Surprisingly, Aero Precision uppers have taken the most lapping to get squared up. Fulton Armory and "no-name" Cerro Forge uppers were pert-near square out of the box.
 

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I haven't squared a receiver in 10 years. Once I started using Mega and then Aero receivers I've never seen one that needed squaring. Before that, yeah, the barrel and the forearm would not always be in alignment but no problems with Mega and Aero, and most other mfg have caught up. Stag are square too these days.
 

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But why wouldn't you square an upper when it only takes about five minutes? I square all uppers on my builds. Maybe they don't need it. But it's a lot easier to do it initially than having to go back and do it after the upper is completed.
This is a fair question. The answer is straightforward. If you are building 1000 uppers that's 5000 minutes which is 80 hours. When you have 100 customers at a time calling and emailing impatient to get their orders every minute counts. It's a matter of opportunity cost and in my experience, since switching to Mega first and then Aero when Mega sold to Zev, I have had ZERO upper receivers that needed squaring, so it amounts to a massive waste of time, all things considered.

Further, there's really no excuse for a company to produce a standard forged upper receiver with a face that isn't square anymore. Modern machines and methods being what they are, if a company can't make a square receiver, they're doing it wrong.
 

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Discussion Starter · #12 ·
Picked up a "squaring tool".
Now I have 4 AR's to debarrel and square up. 😀

Thanks folks!
 

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Picked up a "squaring tool".
Now I have 4 AR's to debarrel and square up. 😀

Thanks folks!
If they are accurate it falls into the category of "If it ain't broke. don't fix it." And another saying, "Sometimes better is the enemy of good enough."

I built three uppers. I have a lathe so for the first I made a mandrel to spin the upper so the face could be machined square. Once the upper was mounted on the mandrel the face was indicated to measure runout. The face was less than .0005" out of square. The other two uppers were the same. None of the three were machined.

Personally, I think if the extension is a reasonable tight fit in the upper and blue loctite is used, the need for squaring is questionable.
 

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This is a fair question. The answer is straightforward. If you are building 1000 uppers that's 5000 minutes which is 80 hours. When you have 100 customers at a time calling and emailing impatient to get their orders every minute counts. It's a matter of opportunity cost and in my experience, since switching to Mega first and then Aero when Mega sold to Zev, I have had ZERO upper receivers that needed squaring, so it amounts to a massive waste of time, all things considered.

Further, there's really no excuse for a company to produce a standard forged upper receiver with a face that isn't square anymore. Modern machines and methods being what they are, if a company can't make a square receiver, they're doing it wrong.
All fair points, and well-taken.

From a manufacturing/professional building perspective, this makes complete sense. If you have trouble with out-of-spec parts, you contact the manufacturer and have them make it right. Or, if they can't/won't make it right, you switch vendors and carry on.

For me, an individual, and not anyone who has customers to worry about, taking that little bit of extra time to square an upper gives me peace of mind and, frankly, I enjoy doing it. But, again, this is just a hobby/pastime of mine, not a business.
 

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This is a fair question. The answer is straightforward. If you are building 1000 uppers that's 5000 minutes which is 80 hours. When you have 100 customers at a time calling and emailing impatient to get their orders every minute counts. It's a matter of opportunity cost and in my experience, since switching to Mega first and then Aero when Mega sold to Zev, I have had ZERO upper receivers that needed squaring, so it amounts to a massive waste of time, all things considered.

Further, there's really no excuse for a company to produce a standard forged upper receiver with a face that isn't square anymore. Modern machines and methods being what they are, if a company can't make a square receiver, they're doing it wrong.
Sure on raw machining they are square but after anodizing the surface is not even anymore there is a small amount of build up , jig one up and spin one on a dial indicator then tell me they are all perfect. ;)
 

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Sure on raw machining they are square but after anodizing the surface is not even anymore there is a small amount of build up , jig one up and spin one on a dial indicator then tell me they are all perfect. ;)
Typical anodizing thickness is less than .002" To see a variance of more than .0005" from the process would be very unlikely.
 

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Typical anodizing thickness is less than .002" To see a variance of more than .0005" from the process would be very unlikely.
True , I just like everything perfect I'm as anal as they come. It drives me nuts sometimes LOL
 

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True , I just like everything perfect I'm as anal as they come. It drives me nuts sometimes LOL
Here is something (or 2) to consider;

The body of the 'squaring' lap spins in the carrier bore. If there is any clearance between the bore and the body, the lapping surface can wobble, be pulled of square, chatter, etc. leaving the face of the extension mating surface less than perfectly flat and also less than perfectly square.

If the bore for the extension is not perfectly in line with the carrier bore, the the squaring lap will actually 'lap' the face of the extension bore off square with the bore for the extension and produce the exact opposite of the intended result.

I watched several videos of people using the squaring lap. I did not see a single video where anyone lubed the lap body and carrier bore. I wonder how much anodizing was removed by running things dry.
 

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Here is something (or 2) to consider;

The body of the 'squaring' lap spins in the carrier bore. If there is any clearance between the bore and the body, the lapping surface can wobble, be pulled of square, chatter, etc. leaving the face of the extension mating surface less than perfectly flat and also less than perfectly square.

If the bore for the extension is not perfectly in line with the carrier bore, the the squaring lap will actually 'lap' the face of the extension bore off square with the bore for the extension and produce the exact opposite of the intended result.

I watched several videos of people using the squaring lap. I did not see a single video where anyone lubed the lap body and carrier bore. I wonder how much anodizing was removed by running things dry.
Amateurs. I always oil the body of the lapping tool before I insert it. Anyone can make a youtube video. That doesn't mean they know what they are doing.
 

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Here is something (or 2) to consider;

The body of the 'squaring' lap spins in the carrier bore. If there is any clearance between the bore and the body, the lapping surface can wobble, be pulled of square, chatter, etc. leaving the face of the extension mating surface less than perfectly flat and also less than perfectly square.

If the bore for the extension is not perfectly in line with the carrier bore, the the squaring lap will actually 'lap' the face of the extension bore off square with the bore for the extension and produce the exact opposite of the intended result.

I watched several videos of people using the squaring lap. I did not see a single video where anyone lubed the lap body and carrier bore. I wonder how much anodizing was removed by running things dry.
That's interesting. I've always -- always -- drizzled some 15W-40 Mobil 1 on the lap body, smeared it into a nice, even layer, then inserted it into the carrier bore. Using a thicker oil like that tends to support things better, and keeping the whole mess as close to vertical as possible helps prevent any unwanted angles being introduced.
 
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