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Why won't my new upper receiver lock/close on my new RRA lower receiver?????????
persimmonpete  [Team Member]
I'm not sure if this belongs here or in the Build it forum, but here goes.

I got a new RRA stripped lower and finished it yesterday. Upon attaching the upper, I discoverd a VERY tight fit around the rear takedown pin between the lug on the upper and the slot in the lower. In fact, it was so tight I had to use a rubber mallet to get the upper / lower to shotgun open and would never close 100%!

Well, I studied it some today and decided to just machine it to fit. So out comes the Dremel tool and off comes the aluminum around the area where the lug on the upper goes down into the lower. (cutting out the lug relief area on the lower).

BTW I had tried several uppers and all did the same thing. The upper would lack about 1/4 to 3/8 inch closing. Finally got it cut out so it will now allow any upper to close on that lower.

My question - has anyone else seen this kind of problem? In all my builds, I never had. It looked like they just didn't get the lower machined out in the rear area. Unless I hear different, I think that will be my last Rock River stripped lower.
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AKsRule  [Team Member]
Rock Rivers are known for their tight lowers.
(hm . that sounds ghey )
Lets say tolerances

I have one that requires a good hand smack to close or open ; not a biggy.
How much did you have to remove? Maybe you just got one on the high end of Tolerance?
j3_  [Team Member]
Many lowers have two cuts at the two rear edges of the lower that are a little wider than the main cut out portion. This allows the upper to close without a problem. The RRA/CMT made lowers I have do not have these cuts and fitting problem seem to be caused by it. Some file the two back corners of the upper lug. Sometimes just opening and closing it will cut the channels in enough to allow the upper to close. Sometimes they fit. I buy the lowers now from companies that have the extra cuts in them.
persimmonpete  [Team Member]
I probably removed 1/32 inch or maybe a bit less. Before I started it did not have the channels at all.

Again, this one wasn't just hard to close. I had to use a punch to wedge the upper down and a pretty good smack with a rubber mallet to break it open. I did this maybe 10 times before I decided this wasn't going to just ease up with a few cycles.

I checked a std RRA (got it as a complete assembled weapon) and it had some material removed prior to anodizing by the factory. Curious.

EDIT - J3_ yeah that is a good idea about buying the ones I know are cut. Next time I'll do just that.
Kooter  [Team Member]
I just assembled my first RRA lower last night. After getting it all together I had the same problem. The upper I was planning on using would fit about half way into the lower, then get stuck. My bushmaster upper would not go on at all. I got out my files and went to work. They all fit now

I won't use a lower without the relief cuts again.
jcmios  [Member]
RRA addresses this in their FAQ's and suggest a rubber mallet to help close the upper and lower a few times until it can be done without the mallet. I have a few that aster years of use are still nice and tight, I prefer it that way.

Jim
HENDOG1972  [Member]
Got a link to there FAQ page?
DaFuzz62  [Member]
The following is from RB Precisions website. I use this method during assembly rather than removing metal from the lower receiver or the upper receiver lug. Works every time.

All of the Rock River Arms lowers are an extremely tight fit, they need to be worked in the following way :


For the love of God make sure there is no rounds in rifle and it is on safe, the hammer will need to be back in the cocked position!!! Our lawyers make us tell you that death is possible if this is loaded when you perform this, we like our customers please do not shoot yourself!

1. Assemble the front pivot pin to the upper.

2. Lubricate the rear lug completely with a light grease (best) or oil, lube the inside of the receiver also.

3. Ensure the rear takedown pin is completely out in the open position (detent is holding)

4. Slowly push the 1/2's together, they will stick (THIS IS NORMAL) it will most likely not close completely at first this is normal.

5. Open and close, repeat being careful to keep the halves aligned, do not slam them together but continue to use increasing force to fit together, when almost completely together use a nylon or soft rubber mallet to tap upper receiver into final position.

6. When they are seated (little to no gap between upper and lower) lightly tap the rear takedown pin into place. This will seem scary to a beginner but it is natural for a tight fit.

7. You may see some of the anodized removed from the rear lug at the corners, AGAIN, this is normal.

8. You may have some difficulty separating the upper and lower, with barrel up and rifle unsupported (hanging in the air) grasp the rifle by handguard and give a "smack" to the top of the buttstock, you may need to do this repeatable, usually 5-10 times will do the trick.


The guys at RB Precision are very helpful. THeir website has alot of good info too. Hope this helps!
yekimak  [Team Member]
I had a stag lower that was like that at first, but after a trip to the range it was fine.
sobrbiker883  [Team Member]
Boy I wish I read this thread before I put together my pistol on a SunDevil lower.

Real tight. I got them together, and was damn near unable to get them apart. I decided to stone the rear tab on my flattop upper that came used with the pistol barrel as I always revert to my WECSOG mantra: "modify the cheapest part first!!"


RRA addresses this in their FAQ's and suggest a rubber mallet to help close the upper and lower a few times until it can be done without the mallet.

-I will be replacing the upper receiver once I get all the bugs out of the lil bugger then I'll follow RB or RRA's advice.........

HardBoiled  [Member]

Originally Posted By DaFuzz62:
The following is from RB Precisions website. I use this method during assembly rather than removing metal from the lower receiver or the upper receiver lug. Works every time.

All of the Rock River Arms lowers are an extremely tight fit, they need to be worked in the following way :


For the love of God make sure there is no rounds in rifle and it is on safe, the hammer will need to be back in the cocked position!!! Our lawyers make us tell you that death is possible if this is loaded when you perform this, we like our customers please do not shoot yourself!

1. Assemble the front pivot pin to the upper.

2. Lubricate the rear lug completely with a light grease (best) or oil, lube the inside of the receiver also.

3. Ensure the rear takedown pin is completely out in the open position (detent is holding)

4. Slowly push the 1/2's together, they will stick (THIS IS NORMAL) it will most likely not close completely at first this is normal.

5. Open and close, repeat being careful to keep the halves aligned, do not slam them together but continue to use increasing force to fit together, when almost completely together use a nylon or soft rubber mallet to tap upper receiver into final position.

6. When they are seated (little to no gap between upper and lower) lightly tap the rear takedown pin into place. This will seem scary to a beginner but it is natural for a tight fit.

7. You may see some of the anodized removed from the rear lug at the corners, AGAIN, this is normal.

8. You may have some difficulty separating the upper and lower, with barrel up and rifle unsupported (hanging in the air) grasp the rifle by handguard and give a "smack" to the top of the buttstock, you may need to do this repeatable, usually 5-10 times will do the trick.


The guys at RB Precision are very helpful. THeir website has alot of good info too. Hope this helps!


Did this twice now. The second was an extremely tight fit that didn't allow it to come anywhere close to fitting together for a while. With a little work doing the above and a little time, it fit. After shooting a few hundred rounds through it everything loosened up just slightly all is well. Both my builds fit like a glove with absolutely NO PLAY and do not require any extra force, hammers or any other bs to take down.

Both are now perfect.
Zhukov  [Team Member]
One other thing to note is that the recoil spring tube can project forward far enough to prevent the two halves from closing. I built a Stag lower with a 6 pos. CAR stock, and the buffer tube projected forward about 1/64th of an inch and prevented the upper from closing. Unscrewing the tube one complete turn was not really a good idea, as then the tube barely held in the buffer stop pin and spring. A better solution was to remove the tube and use a belt sander to shave off that little bit of extra material at the end of the buffer tube.

Now i'm just down to the tight fit problems everyone has probably experienced. No big deal - tap in the takedown pin with a rubber mallet, shoot it a few times, and it'll fit like a charm...
FMJ  [Member]
I wouldnt machine off any of the Uppers

they are Fine

RRA Lower is the Problem!

A EXTRA EXTRA Tight Fit doesnt Help Accuracy at all!!

My bushmaster is petty tight and I have to use a PUNCH to DRIVE the pins out.

Finally got a LMT Lower and it fits NICE I can push the pins out without a punch !

I think RRA should go MIL SPEC like Colt,LMT,Bushmaster except for my odd one
pantera1994  [Member]
...
Zhukov  [Team Member]

Originally Posted By pantera1994:
Are all RRA lowers like that? I was going to use one in my next build but I'm not so sure now.


There is nothing wrong with RRA lowers. The same thing happened with a Mega and a Stag lower with all RRA uppers, but you have to realize that there might be *slight* variations in manufacturers tolerances.

Contrary to what FMJ said above, I did NOT advocate messing with the lower. In my case, the BUFFER TUBE from my collapsible stock projected forward too far when screwed in to align the stock correctly (and hold in the buffer retaining spring/pin). In that case, I ground off a little bit of the buffer tube to fit flush with the lower.
greco  [Member]
Man, it scares the hell out of me to force parts together and beat with a mallet. On the 6 RRA lowers I have used, the uppers were too tight, so I just took a file and removed just a tad from the rear and lower corners of the rear lug. It works well, and still leaves you with a tight gun.
Krackels  [Team Member]

Originally Posted By FMJ:
I wouldnt machine off any of the Uppers

they are Fine

RRA Lower is the Problem!

A EXTRA EXTRA Tight Fit doesnt Help Accuracy at all!!

My bushmaster is petty tight and I have to use a PUNCH to DRIVE the pins out.

Finally got a LMT Lower and it fits NICE I can push the pins out without a punch !

I think RRA should go MIL SPEC like Colt,LMT,Bushmaster except for my odd one


And I thought I was the only one. My Del-Ton upper and Stag lower fit is so tight I can only move the rear takedown pin with use of a mallet and pins.
buckmeister  [Member]
My RRA upper ONLY fits in my CavArms MKII lower, and even there, it is TIGHT! It will only go halfway in my other lowers. I'll try the RBPrecision suggestion. I thought about replacing the RRA upper; it's nice to know that the fit is normal (for RRA's). I had a different upper that wiggled, which concerned me, though it was no less accurate than the others. Two extremes.

buckmeister
Bubbaguns  [Team Member]
I would rather remove material from the lower so any upper would fit. As far using a puch to remove the rear take down pin, I have a couple of ARs like that. I found that if you remove some of the anodising from the inside of the rear lug hole, the upper and lower can be put together easily. I use a drill bit (by hand).
Dano523  [Moderator]
Guys, the reason that I tacked this thread was to point out that the RRA lowers are tight as a norm, but will mate with upper through normal use/a couple of cleanings.

Now if you have an extensive problem of that of the bottom of the upper receiver lug being a tab bit too long and will not allow the two to mate, then you may need to mill the bottom of the upper receiver rear tab a bit.

Now baring anything short of that last statement, don't file or grind anything down. Use lube and little force and allow the two to mate in with time. Failure to heed this advice will end up with a post in regards to "HOW DO I THIGHTEN UP MY LOWER TO UPPER FIT".
asltrfl  [Member]
I have built at least 20 beautiful AR's using Rock River lowers, they are GREAT! My first time, like you, pissed me off, I thought, "what the hell", but after careful consideration, I decided to lightly dremel the upper corners of the rear lug on the upper. Why the upper and not the lower, well, the upper receiver cost less than the lower, and after dremeling just a little at a time and then applying "aluminum black", you couldn't even tell any work was done at all, I had a better fit than any complete factory gun I have ever purchased, and boy do I love a "PERFECT", tight fitting upper and lower. My builds are a better fit than any Colt, Bushy, or ANY factory rifle I have ever purchased complete. Keep on making them that way Rock River!!
Walkure  [Team Member]
Just wanted to add my personal experience with a RRA lower -

I had no problems at all. Using a complete LMT upper, everything went together just fine, not loose, but definitely not over-tight. No need to use a hammer and punch to remove the takedown pin.

So, not only do other lowers sometimes run tight, but not all RRA lowers are super-tight (though people do seem to have been complaining about tight RRA uppers lately).
Bushman_269  [Team Member]
I had to lightly relieve the rear lug on a Bushmaster A3 upper to get it to close on a RRA lower receiver. I took just enough off to allow a very tight fit on initial closing. Now after some use the parts seem to have worn together sufficiently to allow normal force to push out the takedown pin. As an old carpenter once told me "you can always take a little more off ... but you can't put a little more back on".
Ebbsnflows  [Member]
Dang, I wish I would've read this post 2 nights ago. I just bought 2 RRA complete rifles. I assembled the first one with absolutely no problem. Everything mated up perfectly. I went to assemble the other and had the exact problem everyone here is discussing. It wouldn't even come close to mating up. With much apprehension, I got out the triangular file and hit each side of the upper just a couple of licks (just enuff to remove the powdercoat). Voila...fits like a glove now.

Fit and finish on the rest of the rifle is beautiful.
Derek45  [Team Member]
My STAG was the same way.
the_end  [Member]
I'm glad I found this, I thought I might have had a bad batch. I've got 5 new RRA lowers and 5 new factory RRA uppers and none of them fit together. One required the rear take down pin hole on the upper to be slightly widened. The other 4 are going to take a dremel. I started swapping things around and my Armalite, Colt, Superior Arms, and Mega uppers and lowers all fit each other and the RRA uppers with no problems. I'll skip the RRA lowers from now on, I don't care if this is "normal."
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