DPMS Upper on Olympic Arms lower trouble

[RayGun19]

Ok, I'm hoping someone can advise me on here without having to register over on AR15.com to ask just one questions.  A friend came to me with an Olympic Arms carbine.  the upper was junk, and I knew of a buddy selling a nice DPMS upper for cheap.  So my friend went a bought it, and they mate, almost.  The rear take down pin will almost go in.  I'm guessing something like 0.003-0.005 is stopping it from going through.  It's not that the two holes aren't the same size, they are slightly misaligned. So, as a machinist, I would say just ream the holes and use a slightly oversized pin.  But I'm not a gunsmith or armorer.  So I'd like some advise.  The pivot pin fits fine. And the upper and lower mate tightly.  It's just the rear pin.

Oh, and both holes are 0.250 standard pin size.

Advice? (other than throw away the lower LOL.  That's not in her budget).

[Jgun]

I'm not sure what your friends budget is , and I'm NOT a machinist, but on every AR-15 upper I've seen, the takedown pin hole in the upper is always oval with the larger ID oriented on the horizontal axis. So you could open that up .003 without doing anything to the lower. If you start reaming parts, you end up with an upper and lower that can't really mate well to any other uppers or lowers. Have you tried one of the offsett rear pins from JP Rifles? or maybe the Deamon tactical take down pin that expands in the hole when you throw the lever?

[survivalshop]

Where is the upper contacting the lower . Would it be the back disassembly pin lug on the upper ?

How do the upper & lower mate ?  Does the upper close on the lower to the point that there is no gap between them ?

[98Z5V]

Even Olympic uppers are a tight fit on Oly lowers.  I've got one that's a dedicated .22LR gun now.  After seating the pivot pin in the front, I've always had to tap the takedown pin in and out.  I used to live very close to them, so I went down and asked them about this.  From what they say, it's intentional, and it's to keep the upper and lower tight together - no slop.  It's never been easy field stripping that gun.

What on the Oly upper was junk?  Their barrels are usually very accurate, so I'm just wondering.

[RayGun19]

I could tap it in.  But then you have to tap it out.  Which makes for a difficult field strip.

The barrel nut became loose. Something went wrong with the upper receiver, and either cracked or stretched the threads.  The barrel is fine, but the upper is junk.  It was only $300 for the DPMS upper, and it had a MAGPUL MOE rifle length hand guard too.

[survivalshop]

MY preban OLY. is also tight . If you can tap the pin in ( as long as you don't need a sledge hammer & the two receiver mate up correctly ) it should be fine.

It should get a little easier with time.

[RayGun19]

Maybe I'll use a little valve lapping compound on it.  Just on the upper.  Yeah, no sledge.  I'm sure a cleaning rod and a multi-tool I could tap it in and out.  If it's supposed to be that tight, then I'll leave it.

Oh, and yes, there is a tight fit between the upper and lower, with no gaps.

[98Z5V]

  I'm sure a cleaning rod and a multi-tool I could tap it in and out. 

That's wxactly what I use on mine, everytime I need to break it open.  Valve lapping compound would work great. 

I'm looking for mine right now...  <laughs>