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

Gman757

Gman757

Well-known member
I am having a hard time finding the exact 223 upper I want so I am considering putting one together. I have done some research and have found the barrel I want and now I am looking for an upper receiver. I found a Spikes Tactical M4 upper assembly that I may go with. I have one of the their 6.8 SPC uppers and I am happy with it.

During my research I have seen a numerous mentions about upper receiver squaring. According to what I am reading it's not unusual to find an upper receiver that is not square. They sell a receiver lapping tool at Brownells but some posts say you should use a lathe which I do not have.

Should I worry about a Spikes Upper being square? Is there a better upper receiver that I should use? Should I get the tool from Brownells that can be used with drill and lapping compound or should I try to find a smith to send it to that does this? Is there a better lapping tool out there? If I use the lapping tool what grit lapping compound would you recommend ?

Or am I over thinking this whole issue?

http://www.brownells.com/.aspx/pid=20220/Product/AR-15-M16-UPPER-RECEIVER-LAPPING-TOOL

 
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Ideally, one would use a lathe to true up the front of the upper receiver. If you buy one of the lapping tools that Brownells sells, I recommend beveling the end that starts into the upper a bit more, or else you may have difficulty getting it to even start into position. Lube it well with oil, get it close to fully inserted, and then apply your lapping compound to the shoulder on the upper.

All that said, I wonder how much difference truing the shoulder is really going to make to 99.9% of people. I suppose that in order to really do things 'right,' you should true up the shoulder on the barrel that contacts the upper receiver, too. That would certainly require a lathe.

I bought the lapping tool, so I feel compelled to use it every time I barrel an upper receiver now. If I hadn't bought the tool, I don't think I'd worry about it. And in order to answer your question, yes, your Spike's upper is as likely to need this as any other brand.
 
Before you get too excited about truing up the receiver,,,It might pay you to check and see if it really needs it...

Place your barrel in the receiver and visually inspect it to see if there are any gaps between the flange on the barrel after the barrel nut has been snugged down...If you can find some very thin thread, see if it disappears when wound around the joint and that would indicate that it needs 'truing'...If you want another way, apply a very thin layer of Vaseline to the barrel flange and see if it has a consistent transfer to the upper when the barrel is inserted in the upper...Just insert it straight in and don't turn it..

I have an older DPMS that has been set up for competition with quite a few upgrades and I have an upper that I bought at such a discount that I'm reasonably sure that nothing extra was done prior to it's assembly and it shoots almost a good as my competition rig...Maybe 'luck of the draw', but I've never felt the need to change any of it...
 
Instead of using a lapping compound you could use adhesive backed sandpaper...I forget what grit I used, but guess it would be ~200 or 220 grit. Instead of trying to cut the sandpaper into a perfect circle for the lap tool, I just cut several small pieces and stuck them on there.
In addition to what OT mentioned about checking for square, I could visually tell mine was out of square by just setting it on a table..a small square proved what I was seeing.
I think I might have posted a couple of pictures of the job, inc. a pic. showing the high side before the job was finished.
 
Originally Posted By: Gman757I am having a hard time finding the exact 223 upper I want so I am considering putting one together. I have done some research and have found the barrel I want and now I am looking for an upper receiver. I found a Spikes Tactical M4 upper assembly that I may go with. I have one of the their 6.8 SPC uppers and I am happy with it.

During my research I have seen a numerous mentions about upper receiver squaring. According to what I am reading it's not unusual to find and upper receiver that is not square. They sell a receiver lapping tool at Brownells but some posts say you should use a lathe which I do not have.

Should I worry about a Spikes Upper being square? Is there a better upper receiver that I should use? Should I get the tool from Brownells that can be used with drill and lapping compound or should I try to find a smith to send it to that does this? Is there a better lapping tool out there? If I use the lapping tool what grit lapping compound would you recommend ?

Or am I over thinking this whole issue?

http://www.brownells.com/.aspx/pid=20220/Product/AR-15-M16-UPPER-RECEIVER-LAPPING-TOOL



Ask Mike Milli at D-Tech if he'll square it up for you. He already has the fixture and I doubt he would charge you much to true it up, it's a pretty simple job (unless he's just totally buried in work).

If he did it, you would know it was right.
 
Thanks for the input guys.....

Lurker.... I thought about that. I have seen information about D-Tech squaring uppers but I also see how busy they are, so I figured the squaring tool from Brownells might be the way to go.



 
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I think it is something that should not be overlooked any time you put an upper together. Its not always a problem but sure can be and squaring it up definently will not hurt the accuracy. My gun smith charged like $30 I think and after spending hundreds on the barrel and other parts its a small price to make sure they are all working to there potential.
 
I've had it make the difference between a mediocre shooter and a tack driver. Same barrel, everything the same except for taking it apart and squaring the upper.

It all depends on if it's out of square to start with.
 
Originally Posted By: Gman757Thanks for the input guys.....

Lurker.... I thought about that. I have seen information about D-Tech squaring uppers but I also see how busy they are, so I figured the squaring tool from Brownells might be the way to go.





Yeah, I'm not sure how accurate the various "squaring tools" are.

I did talk with Mike about how he did it, and that's the best way to go.

If you could find a squaring tool that was a precision fit full-length in the upper, you would end up with a good job, though.
 

Lurker.....

I agree that the accuracy of the tool is a big consideration. I did a lot of reading various threads across the web and found some negative comments on the units at Brownells and Midway. I found another source that seems to put out a high quality lapping tool.

I ordered one yesterday.

http://shop.pacifictoolandgauge.com/inde...roducts_id=1139

There is another style squaring tool I found at Brownells but it's more expensive and looks a little "aggressive" to me:

http://www.brownells.com/.aspx/pid=20449/Product/RECEIVER-FACING-CUTTER-PILOTS
 
Originally Posted By: Gman757
Lurker.....

I agree that the accuracy of the tool is a big consideration. I did a lot of reading various threads across the web and found some negative comments on the units at Brownells and Midway. I found another source that seems to put out a high quality lapping tool.

I ordered one yesterday.

http://shop.pacifictoolandgauge.com/inde...roducts_id=1139

There is another style squaring tool I found at Brownells but it's more expensive and looks a little "aggressive" to me:

http://www.brownells.com/.aspx/pid=20449/Product/RECEIVER-FACING-CUTTER-PILOTS




Try this one from Brownells: BROWNELLS

It is the same tool from PT&G. The other is way to agressive for the weekend hobbyist.

Greg
 
IMO, as long as your lap is not terribly sloppy in the hole, you will be plenty square enough..just having a `flat` surface is going to help a bunch.
 
Pretty simple to find out if you're over thinking it or not. Remove your barrel nut and see if the flange on your extension is mating flush with the face. Equally, you could buy the $35 lapping tool, and place it in the receiver, then spin it to see if it maintains contact evenly. If it DOES, then leave well enough alone. If it doesn't, then add the polishing compound and spin it flush.

The cutting pilot is a more aggressive tool. Personally, if I had a receiver so out of true that I needed a cutter, I'd probably return/exchange it. If I could not do so, then I would buy the cutter, turn it by hand with a T-handle (well lubricated), then use the lapping tool from the original post to finish up the cut and clean up the face.

You can also use the original lapping tool to somewhat polish the internals of your receiver. Just add polishing compound to the full length, instead of gun grease.

If you DO use the lapping tool, grease the heck out of the shank, and orient it so the ports (ejection port and bottom) are pointed up so you're not drooping grease out the bottom.
 
Just a little followup for the guys that offered advice:

As I stated before I bought the squaring tool from Pacific Tool and Gauge
. ( I am a little hardheaded) I also bought my upper receiver and decided to go with a Vltor MUR upper. These are supposed to be a little thicker walled and well made.

I don't have a machine shop so the only way I knew how to check for square is with the squaring tool itself and the thread idea from OldTurtle . I lubed it up and worked it into the upper all the way to flush with the barrel nut threads. I then took a very thin piece of thread and tried to work it in between the upper and the tool to see if there were any gaps.

It was nice and tight all the way around so I kept easing the tool out and checking with the piece of thread and applying a fair amount of force to the thread as I did so trying to force it into any gaps. The thread showed the same clearance around the complete circumference of the upper face at various depths. I'm calling it square......

It is probably a waste of time.....but I know now, and if I check my next upper receiver and it needs lapping, the tool is my tool box. $30 for the tool did not break the bank.

square2.jpg



I used both hands and pushed the thread into the seam 360 degrees. Just holding it here for the pic.


square1.jpg
 
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Looks like your good to go then. I wouldn`t call it a waste of time considering how far off mine was..(and why would a builder of fine rifles go through the trouble of squaring them if it wasn`t worthwhile?). At least you now have a method of both checking and truing if you get one thats not so square.
Good luck with the build, and thanks for the update.
 
I 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?
 


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