AR Build Question.....Squaring an Upper Receiver??

Originally Posted By: YotecallrI guess it's ok to square up a receiver, but not needed. Companies like RRA and Noveske don't and they shoot pretty well. After all you're not building a racing engine, you're just slipping in the barrel to the receiver and tightening the barrel nut. And what would the difference in accuracy amount to?

Yotecallr......

You'll get no argument from me as to whether it's necessary or not.

When I decided to venture into building my own I ordered a few manuals and did some research to find out which tools I needed and how to properly go about it. There is a good bit of info out there from both sides of the fence on this.

Your statement itself is the reason I decided to check my uppers...."you're just slipping in the barrel to the receiver and tightening the barrel nut". Since joining the barrel to the upper is the basis for the rest of the build why not make sure it's the best that it can be?

I need the most accuracy I can achieve from the upper to help make up for my shooting.
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After all you're not building a racing engine, you're just slipping in the barrel to the receiver and tightening the barrel nut. And what would the difference in accuracy amount to
....I guess that all depends on your intended use and to what degree you like perfection....

My competition rig has been tuned as much as I can figure out to insure that is will hit where aimed...As with my reloads, the best that I can produce will suffice, but anything less becomes an exercise in futility....

When I was younger and into performance muscle cars, the same thing applied...It's a little embarrassing to be sitting along he side of the road due to a sloppy rebuild while the rest of the guys are out having fun....
 
Originally Posted By: YotecallrI guess it's ok to square up a receiver, but not needed. Companies like RRA and Noveske don't and they shoot pretty well. After all you're not building a racing engine, you're just slipping in the barrel to the receiver and tightening the barrel nut. And what would the difference in accuracy amount to?

It's funny you mention those two builders. I have had them, and many other factory, custom and semi-custom uppers in my shop that simply needed squaring to make them shoot. There isn't any one manufacturer out there that consistently produces an upper that does not benefit from being squared. Most folks that receive an AR that shoots pretty well would have no idea that simply squaring the upper could make that same AR shoot much better. I have been fortunate to work with the AR platform long enough to actually see just what a "before" and "after" difference there really can be.

Accuracy is a linear function. Very un-square = poor accuracy and POI shift when changing bullet weights. A little out of square = pretty reasonable accuracy and very little POI shift. if you are lucky enough to have a great barrel, why would you settle for an upper that only shoots in the .5's and .6's when it could be in the .2's and .3's???

I have squared thousands of upper receivers over the years. Almost every one of them needed at least a little squaring, many of them, if left untouched, would have produced .750" groups with a perfect barrel, perfect ammunition and Venatic doing the shooting....

I came from a background of medical and industrial electronics. Both were VERY unforgiving when it came to mistakes or poor quality parts. If there was ever anything I could do to make a part work better or last longer, I did it. I did anything I could do to help ensure that the machine was going to run well, keep running, and I wouldn't get a phone call because of a problem. That same mindset has stayed with me in my "retirement career" of building AR's and it has served me well.
 
Thanks for sharing that Mike. I know that every little bit helps. The 20 Tactical you built me is one of those one hole guns if I do my part. Nothing better than looking through the scope and thinking you missed the paper knowing you darn sure didn't!!

If I am shooting PD's or trying to hit that one MOA X ring at 500 yards I want all I can get in my corner. I've always had mine squared up and have never had a disappointing bad shooter. Straight and square can't be beat.

Greg
 
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Thank you for posting all the information Mike. The 243 wssm upper I bought from you was extremely accurate and now I now that squaring the receiver IS important. I ordered the tool from Brownells and I have a receiver to use it on, maybe two.
 
I was waiting for a batch of barrels to cool that just came out of the Norrell's oven and thought I would do a little math on receiver squaring.

Shooters often talk and read about "MOA" and I'm not sure how many actually know what it is, so I'm going to start there. Simply put, a minute of angle is 1/60 of one degree. A circle divided up into degrees has 360 equal parts, and each degree has 60 minutes in it, so a circle has 21,600 minutes of angle. If you have a circle that has a radius of 300 feet or 100 yards, one minute of angle is going to be just over 1" or 1.0472". Visualize a triangle that is 1.0472" at it's base, and has two equal sides that are 300 feet long. This is the spread of a 1 MOA group at 100 yards. As the range gets longer, the "1 MOA" group gets bigger. A 1 MOA group at 200 yards is 2.0944, or double that of a 100 yard 1 MOA group.

Where the two 300 foot legs of this triangle come together is the head of your case, or basically your primer-pocket. This means that with a 24" barrel, the muzzle only has a + or - of a little over .003" of an inch to stay within a 1 MOA group.

As you get closer to where those two 300 foot sides come together, the amount of error gets less and less to move the point of impact at 100 yards. On an AR-15, if the front of the receiver is out of square by only .001", it will move the POI about 3.5" @ 100 yards. If it is un-square by the thickness of an average human hair, it will move the POI over a foot!

The average receiver that I square is probably about .002", but they run all the way from perfect to .008" or more. Very few are "perfect", perhaps 1 out of 50.

POI is really irrelevant to accuracy. The part that kills accuracy is the fact that a barrel mounted into an un-square receiver will not allow all of the bolt-lugs to touch. The barrel will be tilted with respect to the travel of the bolt, and it's lugs.

Where I talked about "POI shift" in an earlier post, I was referring to a shift in bullet impact when switching from one bullet-weight to another. In other words, if you have your scope dialed in so that 50 grain bullets are hitting dead on at 100 yards, and the POI shifts 3" to the right when you switch to 60 grain bullets, it may be due to an un-square receiver. I have had many customers notice that when they put a new scope on one of my uppers that they normally don't have to move the adjustments much at all to have it dialed in. That is simply because they are square!

Sorry for the long post, and I hope it helps explain things a little...
 
I wish you had the time to make a sticky on "The accurate AR and what it takes to build one". People would appreciate your talent more, and us garage gunsmiths would do a little better at what we are trying to accomplish. I'm getting my squaring tool today and I can tell you my receiver is not square, because the example of differing bullet impacts you gave is what I'm experiencing. Thanks for the above info Mike.
 
There has been a rather uncanny turn of events in the last hour. I left the shop to pick up the mail, have lunch and do my banking. When I picked up the mail, there was a small priority mail box that contained a customer receiver that was sent to me to be squared.

When I opened the box, I knew I had to square it right away, and I think you will see why....
DSC_0147_s.jpg

Here is a picture of the face of the receiver after being squared. You will notice that there is still some anodizing left in one area. The cutter was touching all the way around at this point, so I didn't cut any deeper. The barrel-extension WILL rest perfectly on the face of this receiver. This receiver really was not bad, I only had to take about .002" off to get it squared.
DSC_0148_s.jpg

The reason why I wanted to square it right away was because of "who's" receiver it was. Like I said earlier, none of them never need squaring.....
 
Originally Posted By: Dtech The barrel-extension WILL rest perfectly on the face of this receiver.

Great write up Mike, thank you for sharing. I quoted the above, because as a novice,( but having decent mechanical ability), I felt this was the key point; perfectly flat with no place to `squirrel around to`.LOL
 
Originally Posted By: DtechIt costs $20.00, including the return shipping. They go out the next day.

Heh, I have a lathe and I wouldn't even do it myself for that price.

The upper Mike built for me I'd put up against any other on the market for accuracy, so he's doing something right. I figure the squared receiver is a big part of it.
 
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