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Squaring up an AR-15 upper


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24 replies to this topic

#1 Dolomite_supafly

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Posted 09 April 2012 - 12:33 AM

I posted this in another post and thought I would make its own thread.

I generally do because the "flat" surface that the barrel mounts to is generally off by several thousandths. And think about it, being off by .001 equates to .1 off at 100 yards and creates additional harmonics when the surface isn't flat. This ensures the barrel is inline with the upper and mated squarely.

Almost every custom bolt action builder squares the front of the receiver as well as the recoil lug. The same should be done to accurize a AR because they are rarely square. Squaring it puts the barrel inline with the receiver and hopefully settles down any additional harmonics.

Here are pictures of one I did for myself:
First I start out with a round tube that is cut to allow for a very tight fit into the receiver where the barrel goes. And I clearance it to allow my cutter to get a full width cut. I make sure to cut a new tube each time to make sure it is true.
Posted Image
Posted Image
Next I start to surface the front portion:
You can see where the imperfection starts to to be cut at the 12 o'clock position. And because this is the high spot it tilts the barrel down and you loose up on your scope, something important for those shooting longer ranges where every click counts. This is normal for the high area to be here first.
Posted Image
This is about 1/2 way there and now the high spot is on the left of the receiver, pushing the barrel to the right:
Posted Image
And finally all cleaned up:
Posted Image

And the reason I do this is because when the gun fires the barrel shifts back against the receiver where it is supposed to be a flat. And in this case the first void is everything except at 12 o'clock forcing the barrel down and creating additional harmonics. Then is settles into the right side of the receiver because the left side has a high spot and again more harmonics. And it is all these varying harmonic frequencies that can cause a gun to seemingly never be accurate.

After doing this the barrel doesn't shift or squirm around upon firing or at least not as much, it comes straight back squarely on the receiver. This reduces the harmonics to only what is inherently in the barrel.

And this receiver had been properly torqued but still had high spots.

And the 20 minutes to do this put me in bed for the rest of the day. Damn I hate my back.

Questions are welcome.

Dolomite
  • JeffsSig likes this

#2 6.8 AR

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Posted 09 April 2012 - 12:48 AM

That makes sense to me, Dolomite. I never thought about doing that. Great post. Thanks

#3 CQB Elite

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Posted 09 April 2012 - 01:09 AM

Great post! I only have 1 question- will you do this to the upper on my build? Just kidding!

I'm building an AR using a Noveske stripped upper/lower set. I've been looking for a barrel and won't be long till I'm ready to put one on. There's no way I have the technical expertise to do this to my receiver but it was an interesting read!

#4 dkd83

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Posted 09 April 2012 - 01:13 AM

Do you find this on all ARs? I am finally going to buy one and wonder if this is something I wiil need?

#5 JeffsSig

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Posted 09 April 2012 - 01:34 AM

Now this is the kind of info and post that should be found on gun forums.
Thanks Dolomite

#6 Dolomite_supafly

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Posted 09 April 2012 - 01:35 AM

Every forged upper I have looked at is like this. I will say I haven't looked at hundreds or even dozens but every one is like this. And just so you know the one in the picture above is a upper with the keyhole forge mark which is the same for probably 75% of the AR's on the market, including some high end guns.

This is the one case in which billet is probably better although I have never checked a billet.

I use a 1" OD tube then turn it down for the receiver hole which, if I remember correctly, is .995" ID. So I basically skim the tube and press the upper in place. The friction holds it in place enough to make a few SMALL passes. Make sure the tube goes all the way into the receiver.

And for the average person this would not a concern and wouldn't warrant the time, effort or money to do. But for those who want to squeeze every possible ounce of accuracy out of their AR this could help.

And just so everyone knows this was my dedicated 22lr AR. I did it because I had the gun apart and figured it wouldn't hurt. It also gave me a chance to take some pictures for others to see.

Dolomite

#7 6.8 AR

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Posted 09 April 2012 - 02:16 AM

I'm going to take my Ranier Arms billet upper apart just to see if that's the case with it. I know it has the tightest
fit of all mine, but that's not what you have described. I believe it to be the case with all the keyhole uppers,
though. The dimensions of those are workable, but they vary quite a bit from one to the next. I never thought
about it being a big deal until now.
EB-SF, you're not thinking about a Noveske barrel? Got a good start on a complete Noveske gun, piece by piece.
Might as well. :D

#8 CQB Elite

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Posted 09 April 2012 - 03:15 AM

I'm going to take my Ranier Arms billet upper apart just to see if that's the case with it. I know it has the tightest
fit of all mine, but that's not what you have described. I believe it to be the case with all the keyhole uppers,
though. The dimensions of those are workable, but they vary quite a bit from one to the next. I never thought
about it being a big deal until now.
EB-SF, you're not thinking about a Noveske barrel? Got a good start on a complete Noveske gun, piece by piece.
Might as well.


I've been looking at the Daniel Defense barrels and haven't really thought about Noveske. My rifle is pretty much Frankensteined- have Noveske upper/lower, DD LPK, Magpul grip and stock, Spike's mil-spec buffer tube, BCM BCG and charging handle. Had to take a break for a while and now its time for front end stuff. Want to get it finished really bad.

#9 6.8 AR

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Posted 09 April 2012 - 03:22 AM

I feel your pain. All of mine are Frankensteined! :D Order a part here and there, wait for them to arrive, play
on internet, do chores, wait some more, etc. Finally one gets halfway built!

#10 CQB Elite

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Posted 09 April 2012 - 03:28 AM

I feel your pain! Its also easier to fly the parts in under my wife's radar if I do them a little at a time.....

#11 6.8 AR

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Posted 09 April 2012 - 05:57 AM

That's always helpful. Their radar is on all the time.

#12 gjohnsoniv

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Posted 09 April 2012 - 06:22 PM

It's also very sensitive, the smallest item will alert them.

#13 Dolomite_supafly

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Posted 09 April 2012 - 08:00 PM

Wow, I must be a lucky man.

She tells me to buy what I want and I am the one who generally has second thoughts. She pushed me to spend the $200 for a suppressor. She has been pushing me to buy a MG for years but I haven't settled into that one yet because of the cost. And anytime I complain about something not being good she tells me to buy something better.

It might be because she likes to shoot as well. She has several guns (actually she has almost as many as I do) and regularly shoots them.

Seriously though, anytime I have been debating on whether to buy something she tells me to just buy it. I don't need her approval to do any buying but I don't need to hide it from her either.

Dolomite

#14 mikegideon

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Posted 09 April 2012 - 08:09 PM

Most of us already knew that Tulip is a keeper :up: .

Now, back to the thread... I'm gonna order this, since I don't have a lathe...

http://www.brownells...ER-LAPPING-TOOL

#15 6.8 AR

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Posted 09 April 2012 - 08:40 PM

Oh rats, I thought you might. I was going to borrow it.

Edited by 6.8 AR, 09 April 2012 - 08:40 PM.


#16 mikegideon

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Posted 09 April 2012 - 08:43 PM

You're welcome to it. Pulling the barrel on my long range rifle is gonna be like a breach birth.

#17 6.8 AR

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Posted 09 April 2012 - 08:45 PM

No, I meant a lathe, but that will do. :D

#18 nysos

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Posted 11 April 2012 - 06:45 PM

So Dolomite,

When do you want me to bring my AR over for this treatment? ;)

#19 mr_b8908

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Posted 26 April 2012 - 06:59 AM

The keyhole marked uppers are manufactured by cerro. As mentioned before, they are seen many high end and low end ar's. Kinda make you wonder how much you paid for a companys name/marking to go next to it.

Great write-up!

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#20 Dolomite_supafly

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Posted 26 April 2012 - 11:58 AM

The upper is a small part of the total cost of an AR. And basing the quality of an entire firearm on only the upper is like basing the quality of a car because of the tires it wears.

There is a lot more that increases the cost as well as quality of an AR other than the upper. And along with the quality parts which do cost more you also get customer service which also increases the cost and value of an AR. That is why a homebuilt AR will sell for less than a comparable factory built gun.

Customer service goes a long way. Look at Leupold scopes, they are far from the best bang for the buck for most of their line of scopes. But what you get with your Leupold scope is probably the best customer service in the industry. And that customer service does have a value for most people.

Dolomite