I just bought a Bushmaster upper M4A3 upper and I am trying to use it with a RRA lower.  It seems that they aren't quite fitting together properly.

After I connect them at the forward-most retaining pin, I pivot the upper back to the rear-most retaining pin.  Just as the little extension that the lip goes through meets the bottom receiver, it stops.  It appears that it is too wide to fit into the lower.  

What do you suggest I do.  I really like this upper and I would love to find a way to make it work.  

Thanks in advance for any suggestions you may have

When you say "too wide", is it hitting the top of the lower and not going in at all,
or is it going in some then stopping?

RRA has a high shelf, some uppers will not seat in the rear.

It's not going in at all.  It's stopping as soon as it meets the lower

[url]http://ar15.com/forums/topic.html?b=3&f=12&t=137896&w=searchPop[/url]

Did a quick search, maybe BM is having a bad batch of uppers???

Did you try posting this in the Bushmaster Industry Forum? I'd call BM.

I'll do some more searching....

One or the other of these pieces are out of spec., I could be a clown and suggest that the RRA lower has been milled to match the new super secret Military specifications, but I won't.

Suggest ya check the Bushy upper w/ a friends lower, (what-ever the make), if it matches up you'll know that it's the RRA lower which is out of spec. If the Bushy upper [b]fails[/b] to fit w/ another Bushmaster or Colt or DPMS lower than it's safe to assume that the upper was not manufactured by Bushmaster and you have a Franken upper......w/ a Bushmaster barrel.

Should it turn out that the lowers the problem:

Does this lower have a matching upper that fits w/ no problems?

If it doesn't, was this lower purchased stripped and built by you or a friend?

Depending on these answers, if material need to be removed on lower was minimal I'd remove it, if it needs alot of removal, I'd seek the advice of a trusted gunsmith.

Basically your first priority should be to determine WHICH half is out of spec....

Mike

Yes, the retaining pin is all the way out.  It just seems as though the lug that the retaining pin goes through may be a hair too wide.  I spoke to someone at RRA who advised that is probably the case and that I should take some very fine sandpaper to where the lug is meeting the lower.  

He advised that he has heard of this before.

Mr. Wilson

I purchased a complete RRA rifle and the RRA upper fit fine.  I went with a different upper because the RRA upper had the permanently attached tactical carry handle that I didn't care for.

I have a Bushy upper that will not fully close up on my RRA lower.  The rear lug that the pin slides through is a little too long on the Bushy and/or the RRA shelf behind the trigger group is a little too high.  This seems to be a fairly common occurrence lately judging from a thread a few weeks ago.  

My RRA lower works fine with Fulton Armory uppers and the Bushy lower works fine with all the uppers I have tried on it. No room for an accuwedge with any of mine.

Try a search a you can see several recent comments on this topic and proposed solutions.  It shouldn't be a major problem to fix but I would let a gunsmith or Bushmaster do it.

Well, after using some #320 sandpaper and a hell of a lot of patience, I was able to get the upper to matchup with the lower.  It is still kind of tight but hey, I won't need an accu-wedge.

Thanks to all who took the time to help a guy out!