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9/22/2017 12:11:25 AM
Posted: 10/31/2003 1:20:50 PM EDT
Guys,

This last weekend I had a chance to purchase a RRA
lower with their NM two stage trigger.

Luckily I tried to fit my DPMS upper onto it before purchasing it.

To my amazement the rear mounting hole on the upper would not line up with the rear locking pin in the lower.
Looked like about an eight of an inch to three sixteenths off.

Question: Is this a common occurance? Would it be cost effective to have either/or both the upper and lower machined to fit?

I know that the ar's are supposed to be built within certain tolerances but was this just a "lemon"? lower.

BTW ,, the DPMS upper fits and fires perfactly on my Colt lower. Just wanted to get another lower so my son could start shooting matchs with me next summer.

Thanks for your help.

Nick
West Virginia

Link Posted: 10/31/2003 1:48:49 PM EDT
The "floor" below the rear takedown pin on the RRA lower is sometimes a little high. There were some posts a while back about them not working with some Bushy uppers (but working fine with others).
Link Posted: 10/31/2003 2:39:15 PM EDT
When I first read this, I thought you meant the center-to-center distance...... But gregw45's reply jogged my memory on this prob... Can you measure from the top plane to the rear "shelf"??? It should be .630"... Easy to machine to size. BTW, I've seen a few uppers that would not fit because the lower was machined "round" with a 1/2" diameter at the rearmost part of the rear takedown lug cavity, instead of "squared", with clearance for the takedown lugs' corners, without cutting into the buffer stop hole...
Link Posted: 10/31/2003 4:09:03 PM EDT
It is probably not the height of the rear deck that is the problem. The issue with the height of the rear deck concerns NFA users with RDIAS or RLLs installed. Their isn't enough clearance below the takedown pin to allow the installation of these devices. RRA lowers are made very tight, even when using RRA uppers. There are 2 possiblilities: 1. The width of the opening in the lower is too narrow. 2. The radius of the rear opening is causing the back edge of the upper takedown lug to rub. You can tell which problem it is by looking at the rear of the FC area in the lower and check for rub marks. In either case, the recommended solution is to firmly press the upper into the lower. Sometimes this involves leaning heavily into it, putting your full weight on it and it will snap into place. Some have used a rubber mallet. It will require a slap of the palm of your hand to open it. The area will open up afer a few hundred rounds and after opening/closing it a number of times and will leave you with a good fit between upper/lower. Another solution is to locate the rub marks on the lower and remove metal from the matching area on the upper lug. Some have removed metal from inside the lower. Personally, I prefer not to remove any metal and just let it work in on its own.
Link Posted: 10/31/2003 8:09:14 PM EDT
I used to run into this problem frequently with stripped Olympic lowers made back around '90~'96 and and non-Olympic uppers. I think they were just drilling the rear takedown pin in a slightly different spot. (Of course, you didn't have this problem if you bought a "matched set" upper/lower because I think they drilled the rear hole with the upper in place.) I've still got a few pre-ban Olympics like this, and since the lowers were too valuable to start grinding on, I just modified the uppers by using a small round file and enlarging the rear hole in the lug. I believe in every case I had to remove metal at the bottom/front of the hole in a line toward the selector. Sometimes you could barely notice the "adjustment" and other times the rear hole in the upper lug looked like a Figure-8! Curiously, though, none of these "fitted" uppers had any problems fitting on other lowers or being loose because the material wasn't removed from the very bottom of the hole, so I usually lucked out on that one. If you decide to try this, be sure to fit it so the rear takedown pin is very tight because it will tend to loosen up after a few hundred rounds.
Link Posted: 10/31/2003 9:15:47 PM EDT
This used to be a common problem, As a matter of fact back in the mid 1980 the only uppers & lowers I owned that fit properly (With out Having to hand fit) were the matched sets Olympic Arms used to sell ( I think I paid $125 for the set); I had to file to fit every one I owned!
Link Posted: 11/1/2003 4:37:32 AM EDT
Originally Posted By neilfj: In either case, the recommended solution is to firmly press the upper into the lower. Sometimes this involves leaning heavily into it, putting your full weight on it and it will snap into place. Some have used a rubber mallet.
View Quote
Note that Neilfj has developed the experience and the "eye" for doing this. If you do it, be careful because it is possible to damage the lower's pin "ears" by applying too much force if it is binding at the front rather than at the rear.
Link Posted: 11/1/2003 6:08:18 AM EDT
[Last Edit: 11/1/2003 6:09:02 AM EDT by thebloke]
I have two Olympic lowers I have already built into guns with A2 uppers and I started on my third gun. I mounted a 20" hbar on a flat top upper I purchased from Model 1 and mounted it to one of my lowers. It wouldnt snap closed. I inspected every noock and cranny on the upper and found the front underside was a tiny bit higher than it was suppose to be.I took a small fine file to the areas and shaved of a tiny bit on both sides. I did this a couple of times until it fitted flush to the lower.I then touched up the filed areas and hey presto. The rear pin fits a bit tight but not overly so and will probaly loosen with use. I havent fired the upper yet Im still building the rest of the gun. It was a surpise to find it didnt fit first time, but I had already assembled the barrel to the upper and didnt realy want to take it back off, especialy when I had fitted it it indexed exactly to the correct hole to line up the gas tube as if by a fluke of good luck. Next time I will fit the upper to the lower before i do anything eles.
Link Posted: 11/1/2003 7:29:28 AM EDT
RRA lowers run tight and most people like this. I had only one upper so far that would not close. A current production Olympic upper. I had to shave the sides of the lug on the upper a bit and it fit right in. Dab some fingernail polish on the possible tight spots, open and close a few times and file on the wear points on the upper reciever. You will like the tight fit once the rifle is assembled.
Link Posted: 11/1/2003 2:12:00 PM EDT
Thanks for the replies guys !! So, would this (fitting and filing process) be something that I could safely handle or would it be advisable to just take it to a local smith and have the fitting done? Apprieciate all of the great posts. Nick West Virginia
Link Posted: 11/2/2003 6:34:16 AM EDT
Originally Posted By Sparks: Thanks for the replies guys !! So, would this (fitting and filing process) be something that I could safely handle or would it be advisable to just take it to a local smith and have the fitting done? Apprieciate all of the great posts. Nick West Virginia
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If you are able to figure out where the misalignment is--exactly--and are careful and good with tools, you can probably do it yourself. If, however, you don't know where to start filing, you probably shouldn't attempt it. I'm not sure from your posts where the problem is--in the mating of the front surfaces, or in the fitting of the pin holes at the rear. If the upper and lower fit flush, and the front pivot holes line up properly, and the upper isn't contacting the lower where it shouldn't, it sounds like all you will need to do is slightly enlarge the upper's rear pin hole (as a previous post said). If all this is just more confusing, get back to us with your questions.
Link Posted: 11/3/2003 4:22:59 AM EDT
I had this problem with a RRA lower and both my Bushmaster uppers. I did not want to file anything on the upper or lower. I also did not want to beat the rifle with a rubber mallet. Instead, I applied copious amounts of CLP on the lug, braced the A2 upper upside down on a table (had a friend hold it firmly) and pressed down on the buttstock until the holes aligned. After shooting about 200 rounds through the rifle it loosened up a bit, but I still had to brace the rifle and apply pressure on the buttstock to get it to close. Another 200 rounds and I can now close the rifle without bracing it, but the upper to lower fit is nice and tight.
Link Posted: 11/3/2003 1:32:46 PM EDT
From what I have seen all the 0-80% receivers are cast not forged and cost arround $80.00 you may as well just buy a 100% olympic arms cast lower for $82.00
Link Posted: 11/3/2003 1:44:10 PM EDT
From what I have seen all the 0-80% receivers are cast not forged and cost arround $80.00 you may as well just buy a 100% olympic arms cast lower for $82.00
View Quote
JustL00king, maybe I'm a little dense, but what does that have to with anything???
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