Ok, so I just finished building a complete lower based on a RRA Lower using the RRA LPK. I don't have an upper for it yet, but I do have two other ARs. I wanted to test fit my RRA lower so I tried to put my Bushy M4 upper on it. The front pivot pin went in just fine, but when I tried to get the rear takedown pin in, it just wouldn't go! At first I thought I had a bad Lower, I have heard of people who had been getting mishaped lowers, just not RRA, so I was surprised. I then tried my Model 1 upper on the RRA Lower. It fit just fine!
    After some careful inspection I found that the "shelf" between the selector switch and the take down pin hole was very shallow on my RRA. It is so shallow that the tab on my bushy upper is hitting on the shelf causing the takedown pin hole not to line up properly. It is about 1/20" off. The rear tab on my Bushy upper is just a bit longer then the tab on my Model 1 upper.
Between my 3 lowers , the RRA is the most shallow, the shelf is actually right above the level of the selector switch. The DPMS is a bit deeper, the shelf is about level with the top of the selector switch. The bushy shelf sits the deepest, the shelf is right below the selector switch.
I just figured this info might be helpful for someone deciding what parts to use for their build.. Now you know,, and knowing is half the battle..

So just to recap
RRA LOWER  + BUSHY UPPER = NO GO!
RRA LOWER +  MODEL 1 UPPER = GOOD!
DPMS LOWER + BUSHY UPPER = GOOD!
DPMS LOWER +  MODEL 1 UPPER = GOOD!
BUSHY LOWER + MODEL 1 UPPER = GOOD!
and of course
BUSHY LOWER + BUSHY UPPER = GREAT!


    Has anyone else seen this? (Sorry if this is old news)
    What uppers have you guy successfully fit on the RRA lower? (Just so I know what my options are when I go to the gun show)

RRA lowers are known to be tight.  Are your sure the lug is bottoming out and it's not just too tight due to a slightly larger lug ?  Sounds like the one lug (upper that won't fit) is ever so slightly larger, just slightly.

I bought a TacSol .22lr upper and it would not fit an RRA, an older Denny's, a new with logo Denny's, or a Knight's lower.

The front pivot pin lug was oversized and it would not pivot forward.  I fit WAY too tight if it was set straight down on to the lower and the pins would have to be forced in... but it would not pivot forward after the rear pin was removed.

I had an Eagle/Armalite lower and it fit perfect on that lower.  

I ended up stripping the Armalite lower off my Recce, using the new Denny's lower on my Recce... and using the Armalite for the dedicated .22lr build.

All my RRA lowers have always had a tight fit on the rear pin... needing a tool to push the pin out.  HOWEVER... as time has pasted they have "shot in" and I can remove the pins without using a tool to push it free.

Sometimes I'm disturbed by the lack of tolerance in uppers and lowers. The radius on one of my flattops is visibly off round and prevents it from sitting in a correctly shaped lower. The rear lug on my bushmaster upper is a little far back it seems because the lug will scrape on the back radius in the lug pocket.

I guess this is why people like billet parts so much... Or VLTOR, apparently billet accuracy with a forging.

TIGHT? Doesn't that really mean other than spec?
Why is it that when one manufacturere builds something it's tight and another builds something that's out of spec?
Just another of the universe's many unanswered questions. Since "grasshopper" hung himself, we will probably never know.

I have 2 RRA lowers and 2 different uppers and they all fit and interchange just fine.  Just got lucky I guess, or my lowers were machined on a Tuesday or Wednsesday and not a Monday or Firday :)

I bought a spare RRA upper for a complete RRA rifle. (all parts factory supplied) The rear of the upper would not close into the lower. When I called, they suggested using a mallet to mate them.

Just stating the obvious here, but he tried all the other combos, so I have to assume that the guy knows how to lock up a lower to an upper. If it were as simple as a slap with a mallet I think he probably could have figured it out. Why don't you post pictures to illustrate the problem?

Yep.  They have their receivers, both upper and lower, milled with nearly interference fits.  This makes 'em VERY hard to get together initially.  But after a relatively short time, they will fit together like fingers in a glove.  I'd recommend a little grease on the takedown lug and some gentle rapping with a mallet to get the two together at first.  You may also need to put "more than finger pressure" on the takedown pin to get it all the way in.  This condition is self-correcting.  Just get it together and shoot it.

RRA know they have a problem and have known about it since 2006 as discussed in http://www.ar15.com/forums/topic.html?b=3&f=66&t=282974

Yeah it is off quite a but about 1/20" of an inch about the thinkness of a CD. If I really wanted too I am sure I could take some material off the Rear lug on the upper and make it fit, but I am looking to buy another upper for it anyways. I will try and post some pics this weekend, so you guys will get a better idea of what I am talking about.

Hey thanks! I knew I couldn't be the first person out there with this problem..

My Yankee Hill upper and TI lower were a very tight fit (the TI lower has an adjustable rear pillar however it had no effect) but after a bit of lube and elbow grease they would go together.  After a few matings they go together very easily and fit nicely.  It is a beautiful gun.  I will post pics once I get a chance to finish it (still missing gas block and flash hider/compensator).

I had a Bushy upper that would not go onto any other lower except the one it came with. I tried S&W, RRA, and Spikes. Funny thing is that the Bushy lower would take any uppers.  It was my first AR and I bought other uppers for it.  Only discover it when I had an issue with an SA lower and reached for the Bushy to test fit like you. 10 years after I bought it. One thing I've noticed is that on mine bushy, is that the back hole is a perfect circle where my other uppers they are a little bit more oval.

Just saying it may be the Bushy upper.

The RR lowers are known to have high shelves.

Grit your teeth and take a couple of heavy file strokes on the end of the lug. after it fits hit the bare metal with a black permanent marker (sharpie)

On some of them you will need to knock a corner off a bit also.

This is kinda what I was thinking, only I was thinking a couple seconds on my belt sander. My thoughts were that the belt sander would keep the bottom edge of the lug nice and flat.

Must just be yours.  My RRA uppers and lowers interchange with other brands just fine.  No slop, and not overly tight.

click me  From my understanding, this is hit or miss. I personally purchased a RRA lower and a RRA from two seperate venders, and have a perfect fit. My fried on the other hand did the same thing (both RRA upper and lower) and he cannot fit them together. Little bit of shaving, and he was good to go

Old news check the top tacked thread in the Troubleshooting forum

Does this problem only occur after the lower is built?  I have the following, an older Bushmaster rifle, a Bushmaster 16" upper and a Spikes Tactical dedicated 22LR upper.  I just purchased an RRA stripped lower.  All three uppers seem to fit perfectly in the stripped lower as well as the original Bushmaster lower.

I have had the same issue with CMT uppers on stag lowers

LMT and Colt uppers fit like gloves.

Buy shitty parts get shitty results.

I will never purchase another CMT M4 upper again

What is it about a VERY tight fit that makes these parts "shitty?"  I'm tempted to say that you're saying this because the parts aren't "genuine Colt," but that would be premature.  Further, I'd suggest that using reports on a web forum is NOT a valid statistical method for measuring how common or uncommon "interference fits" for RRA receivers are.  As I posted, MY first RRA was very, very tight, and required a touch of grease on the takedown lug and some tapping with a mallet to get the two parts back together, at least for the first several times I took it apart.  I have seen one report in this thread about RRA receivers not fitting with each other-and that is the very first report of such a problem that I've seen ever.

I have a LMT and a STAG both mount  on RRA lowers, good fit.

News to me that CMT is considered shitty. Considering that CMT supplies many other well known companies with uppers and lowers.

News to me that CMT is considered shitty. Considering that CMT supplies many other well known companies with uppers and lowers.

I have an RRA lower and have the same problem.  I haven't messed with it enough yet though since I haven't started building the upper for it yet.  I tried to mate it up with an extra DPMS flattop I have but it was to tight to fit.  I didn't mess with it yet but know it is going to need fitting or a different upper.  I will probably try out a BCM once I can find one.

fact of the matter is that EVERY CMT M4 UPPER i've ever bought (about a half dozen) have not fit any lowers properly.

this is my experience, not internet hearsay. unlike your CMT supplies everyone else with parts bullshit

Somehow to me "CMT supplies many other well known companies" does not mean "CMT supplies everyone else..."

In what way did your CMT uppers not fit?  Lugs to wide?  Holes off center?  Saying that they didn't fit doesn't exactly explain the specific problem.

I remember I once had a preban or early 80's Oly lower that had the stop sign on it(SGW) and it would not except a Colt mil spec M-16A2 upper or a Bush master M4 upper. I sent it back to Oly and they fixed it for me for free after they found it(they had a fire or something blew up and it was missing).

All these new AR folks make my head hurt

I hope you weren't talking about me sonny because I have been on this site since day one. Under different user names after the great server crash before you were born. I've shot more rounds of 5.56 in 1 year then guys fire their entire shooting career.

Rock Rivers I've built have been tight fits. Had to tap the pins in with a plastic hammer. They wear in with time.

Easy there internet war hero, I wasn't talking about you.