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Upper/Lower Fit

1999 Views 9 Replies 6 Participants Last post by  tinman
Just wanted to move this out of the other thread (http://xcrforum.com/index.php?topic=103.30) and move it here for discussion.

Regarding the upper/lower fit on the XCR: I think i am in a fairly unique position of having 2 different XCR uppers on my same lower (first upper was replaced under warranty, see my afrcom posts.) My two uppers definitely fit different, this second one has a noticeably larger gap between itself and the lower. The gap is largest at the angled section shown in the photo, where it is 1mm. However, there is no place on the entire length of the receiver where the upper and lower actually touch, including the vertical portion at the rear.

The most interesting part I think though is that if I put the halves together without the rear latch (ie: no recoil spring) they mate perfectly, with no gap at all! So it is not the receiver that is causing the gap, but rather the rear latch mechanism that is holding the two halves apart.

With my first upper, when I held the latch and put the two halves together they would go snug and the latch would close without movement of the upper. On the new upper I can feel the latch push the two halves apart slightly when it closes; anyone else notice that as well? I am wondering if its just a tolerances thing or if the dimensions have changed slightly.


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Sorry, I have nothing to add until I get the 7.62x39 upper when it's released.

I'd suspect if the upper/lower fit tight when locked up, then there shouldn't be any issues. But if they are loose when locked up, you may want to call Robarm and find out.
When I get my 7.62x39 conversion kit, I'll certainly let you know how the fit and finish are.

That might be a few months though.

Why would the fit on the upper/lower be different with the x39 conversion?

It's just a change of bolt/barrel/ejection buffer right?
Thats right, all conversion kits use the original upper.

Besides, I'm asking about how your current upper fits, because between the two I had, they fit differently.
Ah, I thought the conversion kit for the 7.62x39 was a complete upper assembly.

Hi Chris,
the gap isn't too bad. It doesn't look much different than most of the guns we send out. A small gap is okay. If the upper and lower didn't fit together right, it would be really quite noticeable.
Hey Terra,

Ya, it appears to fit together just fine. Reason I asked is just because I remember the old one being a bit tighter. The two halves are a perfect match machining wise, its just the latch that holds them apart. I was actually thinking of trying to make some kinda gasket to fit between the two, or even an adjustable latch for the rear.
I just ran across something today that reminded me of the upper/lower fit discussion that went on a few weeks ago.

To wit: http://www.10-8forums.com/ubbthreads/showflat.php?Cat=0&Number=54528&an=0&page=0#54528

Check it out. It's worth reading and thinking about. This is why I don't really have any issue with my XCR rattling a bit.
just thought i'd sneak in my 2 cents worth on this subject. i just got my XCR friday and i couldn't be happier w/ the fit and finish of my rifle. i haven't seen any evidence of any cant or gap bwtn upper and lower. no sight of any problems w/ the anodized exterior. unfortunately, i haven't had the time to go to the range to start my break-in of my rifle due to work.
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