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Old 09-23-2004, 08:01 AM   #1
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problems fitting a Rock River lower with upper

Hey, just got my Rock River Lower reciever assimbled on my AR-15 parts kit. Now I have a problem with upper take down block (rear block with the hole on the upper), sliding in to the rear of the lower receiver. The Block is a little too wide and lower if not wide enough. I hate to file it, but it will not side in without lots of force that I am not willing to use and requires a screw driver to pray it appart (and that's hard to aviod scratching). Any ideas?
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Old 09-23-2004, 10:08 AM   #2
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I've seen posts regarding this over on AR15.com. It seems that RR lowers are a little out of spec and does require some filing of the block to fit. I haven't had any personal experiences with this, just passing on what I have heard over there.
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Old 09-23-2004, 10:49 AM   #3
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I know what you are talking about. I had to use the drill to open up the detent selector hole, and also had to cut the pivot pin spring down. What I don't understand is that it's one of the most praised AR Receiver. Tight fit I guess. I'll look it over.

Looks like I am going to have to file the upper down a hair, but have to ensure that it's the upper I want to keep. Wait until Dad gets home and let him figure it out .
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Old 09-23-2004, 05:43 PM   #4
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My RRA fit was REALLY tight between upper and lower. On the advice of my dealer I simply manhandled the rifle to get them together. I'm talking about beating them together (and apart) with the butt of my hand! I was told that they're all fit up this way (can't verify as fact) and this treatment isn't unusual. Anyway, did this about half a dozen times before the fit was nice. Maybe your fit really needs filing, but this worked for me.
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Old 09-23-2004, 06:35 PM   #5
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Quote:
Originally Posted by Brassheap
I simply manhandled the rifle to get them together. I'm talking about beating them together (and apart) with the butt of my hand! Anyway, did this about half a dozen times before the fit was nice. Maybe your fit really needs filing, but this worked for me.
That's what my dad and I ended up doing (yeah, I still live at home at 21 and just finished school, looking for a job now). Had to round the rear lug off a little and a mill file and then work the two receiver back and forth and lossend up a little. I'll post some pics once I take it out to the range with a full report (bragging) on the forum. That gun is sweet looking! Thanks guys for the help.
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Old 09-23-2004, 10:30 PM   #6
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I have this problem, too. Only with a Bushmaster M-4(gery) upper.

My dealer tells me CMT (Continental Machine Tool) is making the receivers
(both lower and upper) for RRA & Bushy. I called Bushy, the cus. svc.
said they were NOT using CMT, but according to my dealer (and I am in CT) he says he's been to the CMT plant in New Britain CT and watched
receivers being made roll marked for both Bushy and RRA.

The problem is the rear lug on the uppers is not being machine contoured
correctly.

I ordered my first M-4 Bushy upper a month ago. It would not fit onto
ANY lower I had. I compared the lug side by side with an older Bushy post
ban upper that works fine and the difference in shape of the contouring
marks was profound. They didn't cut enough metal away on the new
one.

I sent it back. Bushy sent me another M-4 - - SAME problem. I gave that one to a friend was an armorer and he contoured it for me so now it fits.

CMT (Continental Machine Tool) & LMT (Lewis Machine Tool) are the two biggest AR receiver manufacturers in the US and have multiple contracts
with companies like RR, Bushmaster, Armalite, etc. I don't think DPMS uses them, I believe DPMS makes their own if I'm not mistaken. And, I'm not sure who makes Colt's receivers at this time, or if they make their
own.

Bushmaster and Rock River are NOT manufacturers. They
are assembly shops who subcontract out for all their parts to their "specs"
for their advertised products.
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Old 09-24-2004, 07:38 AM   #7
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Next time before you file, try using a Dremel tool with a polishing wheel and compound, work that along the sides of the rear takedown block on the upper. That will remove the finish thereby thinning the block and making it mirror smooth. This will reduce friction when assembling and disassembling. Would probably help unless it's really out of spec.

Just a note, this procedure also works great on the slide rails of a parked 1911 frame. Reduces friction and improves reliability. Just be careful, go slow, and remember you're just polishing, not grinding.
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Old 09-25-2004, 02:14 AM   #8
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Next time, I am going to find out which company actually MADE the receiver and when before I buy it and find out through my sources
who live in and around New Britain, CT where they are made whether
or not people who knew what they were doing were making them.

The industry is dying.

The companies are hiring idiots who don't know or care about what they
are doing.

This is true of Springfield Armory, Bushmaster and Armalite.

Rock River is better for service and assembly and has totally replaced
Bushmaster amongst serious, competition rifle shooters. And there
is a reason for that.

$500 and two receivers later: I know what that reason is.
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Old 09-25-2004, 08:44 AM   #9
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rear lug measurements on RRA

I am wondering if a new RRA upper will fit my Bushy lower. I measured the opening for the upper receiver rear lug on the bushies(where the push pin goes through) It measured .5005 or just a hair over half inch. I checked 3 bushy lowers and they were identical. I will check 2 Colt M16's and a DPMS M4.

So here is a question for RRA upper owners: How wide is that rear lug? I am hoping that I will not have to do any fitting if I install a RRA upper on one of my Bushy lowers.

What are your RRA measurements?
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Old 09-25-2004, 10:17 AM   #10
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You can't go by that.

Again, RR and Bushy don't MAKE these receivers at all. Continental Machine Tool of New Britain, CT and Lewis Machine Tool do.

It depends on who the machine operator was that day and how they
had things set up to run.

That's why you don't just get one bad one, there's a whole run of bad ones!

The fellow who started this thread was wondering why his upper wouldn't fit onto his lower. Gee whiz, whaddya know? I had that problem, too.

TWICE.

When a company like Bushmaster takes back your "bad" upper, they might just as well (as they did with me) ship you a whole 'nuther "bad"
one again. They probably have 500 just like that!

They're not checking them out. They're just taking what their contractor
made for them, stick in a box and ship it.

It's when the end users (hint, US) have these problems, post them on the net and lo and behold - there's more of us out there with the same problem!

I don't have a digital camera, or a scanner, so I can't post pics. But believe me when I tell ya I sat up for two hours one night going through
three of my receivers, two of which are rollmarked BUSHMASTER and two
more from a friend's collection and the upper would not fit on any of the five. Conversely, the old uppers were perfectly swappable among any
of the receivers we had out.
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Old 09-25-2004, 04:50 PM   #11
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I guess I will wait and see. I see what you mean about quality control with some of these makers. For a long time I would $wear by Bushmaster quality. Almost all my AR15 clones are Bushys. Of the ones I have (made back several years ago) the QC is good. Uppers and lowers swap back and forth with Colt M16s so at least the uper and lower fit is good.

Just imagine what a can of worms it is going to open up if the AR 15 makers keep changing the dimensions of their parts. It is going to be like the FAL with its inch, metric and mixed upper and lowers etc...

As soon as I get mine fitted I am going to give it a rest for a while.
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Old 09-25-2004, 05:22 PM   #12
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As for me, I'm done. I have all I will ever buy my whole life.

I fully expect that we're only seeing a temporary reprieve on this
AW ban.

It'll be back and badder than ever. IF we lose control of the Senate
which we hold by ONE seat! I almost think the Senate election this
year is every bit as critical if not more so than the Presidential election.

Think about it: that upper chamber can ratify international treaties
(like a UN gun ban) and the House would have no say in it.

The only thing I am interested in buying now are repair parts, ammo
and components.

S.1431 would ban every gun we love, including semi-auto shotguns
AND PARTS USED FOR REPAIR OR REFURBISHING (direct text from
both the Senate version S.1431 - which Kerry cosponsored of course-and the House version HR.203
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