The Rock River lower I recently bought won’t mate to either of my Bushmaster uppers.  It appears the shelf at the rear of the lower is too high, therefore the push pin holes can not line up correctly.  The Bushmaster and Eagle Arms lowers I own have a lower shelf and don’t have this problem.

A couple ARFCOM friends informed me that this is a known issue with RRA lowers and Bushmaster uppers.  It was suggested that the problem might really be with the Bushmaster uppers having slightly longer (read: out of spec) pin posts.  (Not really sure what they are called, but I mean the part with the hole for the pin to hold the upper to the lower).

Whatever the reason, I just know my two Bushmaster uppers attach just fine to Bushmaster, Eagle Arms and Armalite lowers but will not attach to a RRA.  I think it sucks.  I had picked out the upper I wanted for this rifle and it happened to be a Bushy upper.  Now I’ll have to either replace the damn RRA lower or buy a RRA upper.  

Any way to fix this?  Can I shave a little off the rear shelf on the lower?  

Are you sure that the rear takedown lug is is bottoming out on the lower's shelf? Reason for asking, RRA is known for having a tight fit in this area, not for having a high shelf (at least not that I've heard of). From what I experienced and have heard others have run into is that the width of the opening of the rear shelf area of the RRA is on the lower side (tighter) of spec, while the takedown lug is on the high side.

On mine, it took a good, firm slap to get the upper to seat fully, and after a few open/closings and a couple hundred rounds of firing, it loosens up so that it snaps together. If this is the case, then you really don't have a problem.

Others have taken the approach of removing very little metal from the sides of the lug, while others have suggested taking a file to the lower. Personally, of the 2 options, removing a little from the lower is probably the best option if you are going to go this route. Since the upper fits on your other lowers, I wouldn't bother taking metal off the upper lug.

We are only talking a few thousandths of an inch, so you don't have to take much off in any case.

In my own case, I liked the tight fit, and after a short time, the opening/closing wasn't an issue.

I've never had a problem mating my Bushy upper to my RRA lower. Although it is normally on a Colt upper.

Hey Book I remember you buying that lower, hope you get things squared away.

ATLGA - yep, this is the lower I bought at the Eastman show a few weeks ago.  I bought an ACE skeleton stock, Jewell trigger and a G27 grip.  The ACE stock was bent and the Jewell trigger was a pain in the ass to install.  This lower has caused me a LOT of frustration at this point.  

Neilfj – thanks for the info.  I did a little searching on this site this morning and found similar comments to what you posted regarding the tight fit.  I compared the shelf in the RRA lower to the Bushy and EA lowers.  The RRA is definitely higher.  Tonight I’ll take another look at it to make sure it isn’t just tight on the sides.  Shaving metal off anything doesn’t really appeal to me.    

cover the reviever with a rag.

tap it with a mallet, gently forcing the reciver down into the lower.

you will need to tap the rear takedown pin in as well.

take it out to the range.

i did exactly these things. it solved the issue.  

Like Neilfj, it took a good firm slap to get the rear of my Bushy upper to properly seat on my RRA lower.  But, once it did and I shot it a bit, it fit very well.

Hope you can get it worked out.

I also think you need to give the tight fit theory a chance. Chances are, its just snug. No one else here ever has had incompatibility issues with RRA, try filing or a hard slap and see what happens.

Yes, the RRA shelf is higher than the Colt or BM, but in the instances I'm familiar with, it doesn't interfere with the lug. (The RRA higher shelf will interfere with the installation of an RDIAS or RLL though). I don't like shaving metal off either, which is why I (and others) recommend the slap/towel&mallet method. I think you'll find that once it creates a slight depression in the lower, the upper will fit nicely (I actually like the tight fit of RRA lowers).  Glad I could help!

There are two different issues here.

1.  Your RRA lower will not line up with your Bushy upper no matter what you do, and the product is defective.

2.  Your RRA lower fits very tight and you have to tap it into place with a mallet anfter slapping it together in order to get it to close.

Which is it?  You haven't let us know if it will fit at all, or if it is just tight.  Version #1 is bad news, and no doubt there will be a slew of other RRA owner/ builders who are going to have the same problems.  Version #2 is something many of us deal with.  If it is a field weapon, file the upper lug a tad.  If it is not a field weapon, leave it alone and tap it in and out like the rest of us.

Stickman –
I’m hoping it’s issue number 2 – a REALLY tight fit.  I’m just not sure.  I’ll look at it again tonight.  

Both uppers I tried had a gap (maybe as much as 1/8 of an inch) between them and the lower.  I used what I thought was considerable force on my A2 upper to try to press the upper and lower together.  I placed the lower on a bench and pressed down as hard as I could on the upper to no avail.  All this did was cause the upper and lower to be so stuck together that I had to bang the top of the stock on the ground to separate the upper from the lower.  Is this indicative of what you guys mean by a tight fit?  Is it normal for a tight fitting upper to have 1/8 of an inch gap between the upper and lower?

I didn’t try the mallet.  Just how much tapping with a mallet is normal?

Had the same issue with the BM upper and RRA lower.  2Minkey's advice in this thread is good. This was the advice provided by both BM and RRA.  The upper 7 lower don't fit at first, requiring the careful use of a rubber mallet, which you're very reluctant to do. The upper to lower fit wears in quickly to provide a tight fit with smooth separation of the upper and lower.

Don't guess, put some little blobs of modeling clay in the receiver, and find exactly where it is touching.  Do the same thing with several other lowers that WILL fit your upper.  This may help you narrow down where there is interference.

I would bet tapping it together and shooting will fit it for you, but at least you should know where it is not fitting before grinding on anything.

Bookhound,

I recently purchased a RR lower and had the EXACT same problem you are talking about.  When I got home, I was excited about trying out the new lower.  I took an upper off of one of my Bushies, and it would go in except for the last 1/16" or so.  I was truly disgusted!!  I posted the same thing here, and was encouraged to use a little force, as the RR lowers were tighter.  I measured it against other lowers, and it definitely was tighter by far.  I took a rubber malet, and using a flat top upper, I rapped it a few times, and got it to seat.  I had to "break" it open over my knee, using both hands a few times.  CLP'd the lug, operated it a few times, and now the Bushie upper will drop right in.  Tight, but it goes in.  I am sure that as it is shot and used more, it'll be easier to open.

Before you get too upset, give it a try.

Good luck, and let us know what happens.

I have built 3 complete RRA lowers and own 1 factory rifle from RRA.

From what I understand about their lowers, they were designed with a higher shelf than normal to make it impossible to install a DIAS or a LL. Get a set of calipers, and DL the blueprints from the ar15.com homepage. Take a few measurments on the lower receiver.

Take a chill pill.

Things will be OK. With my varminter, I had to file a little from the sides of the lug that goes into the lower receiver. I now have a custom fit.

-No accu-wedge needed.
-No tensioning pin needed.

RRA is the best quality and value on the AR scene right now.

yeah, just be smarter than me and make sure you're holding the foregrip far out enough so when it does break open you don't squash yer thumb between the grip and the forward surface of the magwell.

   [LOLabove]I hate when that happens!

I bet you will remember it next time, though!!  Kinda like you only get your thumb mashed in a Garand one time, next time it is out of the way. [ROFL]

Had this problem on Saterday after I got my upper in the mail.  Didn't seat all the way back.  Thoroughly pissed off, thinking I recieved one of the older out of spec uppers, I posted on the "Lowers and Complete" section, under "RRA Troubles".  Basically the issue was resolved with about 5-6 taps with the rubber mallet, thanks to the suggestion of over forumites, including Pete (Legal Transers).  Talk about a tight fight!  I love it.

I bought my Lower at a Georgia Eastman show... defenitely got ripped off, didnt know any better [:)]

~Santi

I haven't tried all the uppers you mentioned, but I have tried BM and RRA and the RRA upper had the same tight fit as the BM did. Nothing required modification, just a some extra pressure and and a squirt or two of CLP. I don't think that BM or RRA is the problem. BM probably mills the lower lug on the plus side of the tolerance, while RRA chooses to build to the lower end of the tolerance spec. It probably only amounts to a total difference of .0002", but it is all that it takes.

I would suggest you buy factory assembled rifles if a bit of filing turns you off.

Re the high shelf, Rock River, and just about everybody else is using them these days. As noted above, it's to prevent the use of drop in auto sears. To my knowledge, only DPMS and Bushmaster are still using the old shelf height on current production.  I seriously doubt it's that height that's causing the problem, but it's easy enough to check. Smear some lipstick on the bottom of the lug, and close the to pieces, giving the upper the rubber mallet rap treatment. If the lug is impacting the lower shelf, you'll have lipstick on the shelf when you separate the pieces.

BTW, if anyone is aware of another brand lower that still uses the lower height shelf, please post it over on the full auto column. You'll have the appreciation of a whole bunch of legal DIS owners[:D]

First of all, I didn't really mean to bash Rock River or their products.  I was just frustrated with what appeared to me an out of spec issue.  After further research it does appear only Bushmaster uppers have the problem with the RRA lowers.  

The advice here worked for me.  A little (okay a LOT) of CLP and a little pressure while trying to mate the upper and lower seemed to loosen things up a bit.  I just couldn't bring myself to bashing the upper with a hammer, rubber or not.  So, I held the rifle upside down and with the carry handle firmly resting on the bench I applied pressure to the stock until I could tap the pin in place.  Viola!  The upper and lower are together and are [b]TIGHT[/b].  

Thanks for all the help.  

Great! Glad to hear everything is Ok!  Now, go shoot it! I guarantee it will be more fun than the assembly [:)]

Good deal Book.  Tight is good, yaknow.[naughty]