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  #1  
Old 10-01-2011, 4:05 PM
melodybliss melodybliss is offline
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Default Upper and lower mating issue - rear pin hole out of alignment

Hi everyone. I just built my first lower (hooray!) to go with an upper I had forgotten about that was in the safe.

When I mate the two together, they go together great... except the rear pin socket in the upper is about 1/16" out of alignment.

Here is a photo of the upper and lower just before mating.



and after mating, with me holding the upper and lower together (to get the lugs to line up as much as possible)



My question is this. What can I do to fix this to get them to mate correctly? At this point, the pin won't go through with hand force at all. The rifle does seem to function. I can pull the charging handle (while keeping the two halves together) and otherwise, the rifle seems to be functioning correctly, though until I can get it to the range I won't know for sure. However, without the pin in, I don't want to do a live fire function test.

Any suggestions would be greatly appreciated.

thanks

Mel
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  #2  
Old 10-01-2011, 4:12 PM
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What brand are the upper and lower?
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  #3  
Old 10-01-2011, 4:17 PM
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make sure your buffer is not screwed in to far.
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Old 10-01-2011, 4:17 PM
melodybliss melodybliss is offline
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The upper is unmarked. So to be honest, I do not know. It was bought from a friend of a friend who was heading back out to be deployed.

The lower is a Stag Arms with Daniel Defense parts.

jamesob, that was one of the first things I had checked. It definitely isn't in too far. The flared lip of the tube traps the buffer retainer spring and it also doesn't block the upper from coming down.

To verify, however, I backed the buffer tube out and attempted to mate the two halves. Still no joy.
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Last edited by melodybliss; 10-01-2011 at 4:29 PM..
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  #5  
Old 10-01-2011, 7:00 PM
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I had this done to a customer of mine awhile back...
http://www.calguns.net/calgunforum/s...d.php?t=456187

easy fix... so easy dont laugh now... just drill it thru than aluminum black it...

the top and bottom fit but pin wouldn't so i got same diameter drill bit of receiver hole and slowly made my way thru... presto pin fit with no other problems...

and honestly really doesn't matter what upper and lower you have that's not going to solve the problem at hand...

Last edited by Milspec714; 10-01-2011 at 7:01 PM.. Reason: add link
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  #6  
Old 10-01-2011, 7:04 PM
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It's hard to tell from your picture, but it looks like there might be some excess material where I've hi-lighted:
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Old 10-01-2011, 8:15 PM
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did you try to flip it upside down
place the upper on the bottom, then lower
try it!!
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Old 10-01-2011, 8:25 PM
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dremmel
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  #9  
Old 10-01-2011, 8:26 PM
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My stag lower and cmmg upper fit really tight. I have to almost hammer in one of the pins.
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Old 10-01-2011, 8:33 PM
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The rear pin on my "cheapo" build (Aero Lower, JSE upper) has to be pressed in/out with a punch.
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Old 10-02-2011, 9:35 AM
melodybliss melodybliss is offline
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killmime1234, I took a look. It looks fine there. I think that's a photo artifact and isn't extra material.

I think I'll end up drilling the area out so that it opens it up by that last 1/16. I'll mark it first with a sharpie to make sure I'm removing only what I need to.

Thanks everyone. I'll let people know how that goes once it's done.
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Old 10-02-2011, 10:38 AM
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The front pin is in place, right? If it were me I would not drill through both the upper and lower at the same time. Mark the upper with a needle or other sharp pick while it is on the lower, separate and either file or dremel the marked portion on the upper. Otherwise you stand a good chance of enlarging the holes in the lower.
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Old 10-02-2011, 11:09 AM
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Is the bottom of the takedown pin hole on the upper bottoming out in the pocket of the lower? Use a black marker or dykem to see if any place is touching.
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Old 10-02-2011, 11:22 AM
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just oval that uppers rear takedown pin hole out with a drill bit

you know insert bit turn on apply force in the direction you need space
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Old 10-02-2011, 11:26 AM
Coyotegunner Coyotegunner is offline
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WTH.Do you have a friend or something with another upper to compare and try theirs on yours.Sorry,just never seen it before.Have only dealt with Colt,Bushmaster,Dpms and recently S&W,BCM.Everything has been interchangeable just fine.Wish you were near me,I would bring some stuff to help you decide your next move.
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  #16  
Old 10-02-2011, 1:47 PM
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Quote:
Originally Posted by waho View Post
If it were me I would not drill through both the upper and lower at the same time. Otherwise you stand a good chance of enlarging the holes in the lower.
MMM.. honestly its the best way.. how else are you going to exactly get rid of the protruding material? its aluminum you can actually turn the bit by hand just with a pair of vise grips holding the bit and some oil...

Quote:
Originally Posted by melodybliss View Post
I think I'll end up drilling the area out so that it opens it up by that last 1/16. I'll mark it first with a sharpie to make sure I'm removing only what I need to.

remove take down pin
start with 7/32 bit with a drill at slow speed and just do a couple of passes to get rid of excess and move up to a 1/4 bit which will fit tight but not enlarge your holes..this is where you use the vise grip by hand trick, like i do go from both sides until you can thru all the way... re-install take down pin and test...
use birchwoods casey aluma black to touch up visible aluminum

hope it works out for you..
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  #17  
Old 10-02-2011, 2:59 PM
melodybliss melodybliss is offline
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So before I start doing any drilling, we pulled the CMMG AR out of the safe and I took it apart.

It looks like it's a lower issue and not an upper. The CMMG lower takes the upper I thought that was out of alignment. The CMMG upper has the same problem on the Stag Arms lower. :/

I'm guessing I should contact Stag Arms for this.

Thanks everyone for your help.

Mel
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  #18  
Old 10-03-2011, 8:36 PM
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Back your buffer tube out one turn. Problem solved.
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  #19  
Old 11-08-2018, 1:35 PM
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Quote:
Originally Posted by Purple K View Post
Back your buffer tube out one turn. Problem solved.
"Amen" to that, Purple K!

Thank you for the simple fix. I was reading all those suggestions to start altering the machine work and even some suggestions to "hand drill" on the lower and it was giving me a serious case of the stuttering WTFs (at least use precision basic garage implements like vices and drill presses, at low-speed if you wish). At least some people (including the OP) were sensible enough to recommend he defer to the manufacturer or a professional gunsmith but your one sentence comment was the greatest of them all.

I was working with a PSA lower (built by me) and a PSA upper (purchased fully assembled) and completely stumped. Now keep in mind, please, this is the first AR15 that I've ever built. Heck, this is the first gun of any kind I've ever built. And my education on the matter is all from the esteemed YouTube University at the internationally renound campus of the WWW. I couldn't imagine I'd had the rotten luck of getting my first purchase to also the rare blem or part that snuck past the QC station. I didn't want to give up and now I'm glad I was patient enough to just keep reading.

Sorry for bumping a post so old it might have been originally written on stone tablets but this really helped a noob like me and maybe it would help someone else too.
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