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Posted: 4/15/2003 7:33:03 PM EDT
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I just rec'd a new Rock River complete factory NM lower, and when I tried to put my uppers on it, it won't close. I have a Colt upper, homebrew upper and 2 Bushmaster uppers, and on none of them will the rear lug go into the lower receiver. The rear lug stops when it tries to enter the lower. These uppers interchange fine amongst themselves, though. I need the specs on the width that the cut in the lower is supposed to be, and what the maximum width the rear lug on the upper is supposed to be. I have read so much about how great the RR lowers are, that I finally ordered one. Now I am having second thoughts. If the lower is out of spec (which it sure seems to be), I am going to call Rock River and see what they will do about it. But I want all the info I need before I get them on the phone. Thanks for any info, Bob |
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Bob, they are a tight fit normally but this one sounds excessive, if you can't get what you need from RRA (shouldn't be a prob) I will try to help you out. (We are 5 minutes from RRA) While there is a minimal amount of tolerance on width and coating buildup it is possible you are at a bad virtual condition (worst case size on both parts.) I will be there tomorrow and can get you the specification for width if you would like. Email be at [email protected] www.sableco.net |
| My RRA lowers didn't like my FN uppers at first either. They where very tight. Had to force them down with upper body weight while they where braced on the bench. They loosened up and shoot real good. They do seem to run tight on fit to uppers. Sounds like you may have gotten an extreme case. |
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Yep they tend to run tight..not a bad thing for accuracy...unless you cant get the halves together... :) Let Robert help you out...great guy...and like he says he is 5 min away from the factory and gets all kinds of neat stuff and information...good insider contact Donny & Robert @ Sableco is good people [email][email protected][/email] [url]www.sableco.net[/url] |
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Well, I got up this morn and took some measurements with the calipers. The RR lower measures .498 at the rear take down pin. My other 4 measure .503-.511. The shelf depth on the RR is .497, on the other 4 it is .632-.643, measured right in front of the rear take down pin, with it pushed through. The rear lugs on all 4 of my uppers measure .500 wide. I read on another thread that another person was told to knock it in with a rubber mallet. I did this, with my Bushie flattop upper, and got it to seat, and was able to get the pin through. To open it back up, though, I had to hold it between my legs with the barrel pointing to the rear, and knock the crap out of the stock just behind the lower, using the heel of my hand. After about 3 or 4 knocks, it finally came open. I am not comfortable with this method because I usually don't carry a rubber hammer with me, especially hunting, which is what I was getting this NM lower for. I am wanting to purchase a new upper for this lower, but am not going to put up with banging and hammering, especially when I have a scope on it. As for the dremel, I am not going there. I paid for a receiver to be in spec, and that is what I want. My other 4 interchange just fine, and if RR and I can't work things out, I will put it up for sale. Thanks for the replies. Robert, I will email you the specs. I appreciate your trying to help me out. Bob |
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Glock; According to my AR15 blueprints, the width of the opening in the area of the rear takedown pin is .500 +.000/-.004 which would give a range of .496 - .500" Your RRA lower appears to be in spec. (For M16 it is .500 +/- .004). As for the depth, this is variable. Some manufacturers put a high shelf in this area so as to make them more difficult to modify into full auto as the DIAS/Lightning Link won't fit under the takedown pin. For both AR15/M16, the shelf depth is supposed to be .630. There is no +/- tolerance listed, since in a Semi-Auto you only need enough clearance for the takedown pin. As for the width of the upper lug, I don't have prints for the upper so can't help you there. What I can tell you is that I had similar occurance with my RRA lower and RRA upper. The fit is VERY tight. I was warned about this when I purchased my lower and told by Pete-in-NH to put my weight on it to get it to close and after a few hundred rounds it will loosen up...and that is exactly what happened. (The rear takedown pin also fits tightly until it loosens up a bit too). It still takes a little "slap of the hand" to open/close it, but nothing excessive. What you are experiencing is exactly the same as mine and I had an RRA upper. I don't think it is a manufacturing problem. The problem is in the tolerence allowance between manufacturers. RRA tends to manufacture their products so that they are midway in tolerence allowances. Other manufactures may prefer upper or lower tolerence limits, and some don't even worry about it in non-critical areas. (Shelf depth is an example). 2/1000ths isn't much. A little CLP on the lug will help and you'll see that after a few hundred rounds it will get much easier. |
| I'll join the others who stated that RRA lowers are a tight fit, mine was also, same situation as yours. I got scared when I couldn't get my receivers seperated! Everythings fine now and still a very solid fit with minimal play between receivers. DO NOT start grinding on things! |
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Another tight fitting RRA lower here. Same thing, front lug was tight, rear lug wasnt going in at all. Eventually worked it in (thanks to the chat room guys while the forums were down) and started shooting. It has since (600 rounds or so) loosened up enough to where I can separate the upper and lower normally. Here's what worked for me -- YMMV: With lugs and pins lubed well, slowly work it in at far as it will go, then pop it good right over the charging handle, back it out, repeat until your arms are sore. Do this with the halves even over the lower (i.e. do not put front lug in then force rear). Use more pressure each time and once it seats and the pin goes through, take it back off and reseat a couple more times. I was pissed was mine came in that way and thought about sending it back to Pete or RRA. A little elbow grease later, I love the damn thing. |
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Well, it looks like I might just have to assemble it, and get out and shoot it. I guess it could be worse.... Seems like I am not the only person that this has happened to. Even though it doesn't seen kosher to me, I guess I will try it and see what happens. I guess I am just spoiled by the other 4 being so easy to open and close, even when they new from the box. Thanks for all replies. Bob |
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