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1/25/2018 7:38:29 AM
Posted: 8/13/2002 4:41:32 AM EST
I have a Bushmaster upper, nothing fancy just an ak74 brake, and A1 sights.

I just received a RRA lower and I wanted to attach the Bushmaster upper.

Nope. The lower will not fit the upper. The front lug on the upper barely fits, and the rear lug is too wide to seat in the lower.

Advice? Suggestions?

Do I lightly file away material from the upper lugs or do I remove material from the lower?

Do I do neither, and just find another upper that will fit the lower.

I have been using this upper on a Bushmaster lower and it fits just fine.
Link Posted: 8/13/2002 4:58:07 AM EST

thats a tuffie !!! i'd suggest trying to find an upper to fit the lower..., any time you start removing metal........, danger lurks !!
Link Posted: 8/13/2002 4:59:47 AM EST
Damn, I've been worried about this kind of issue.
I'm getting ready to buy a stripped lower and build
my first AR. I wonder if these lowers have problems
with any other uppers. My 9mm will be here soon
and I had thought about switching it around with
a few other configurations.
If you don't get a good answer here, you know to call
John over at K2 Sports.
Link Posted: 8/13/2002 6:11:51 AM EST

I agree. I hate to start filing on my Bushmaster upper. It is my main hog hunitng upper, I don;t mind if it gets beat up, dirty, scratched, etc. Resale is not an issue. However, removing metal from the rear lug seems like a bad idea.

Ilikelegs. This lower will be used with my .22 upper and 9mm upper. Both are still under construction in Florida.

I had assumed all lowers/uppers were interchangeable. Maybe that was a wrong assumption afterall?

Thanks guys.
Link Posted: 8/13/2002 6:14:14 AM EST
RRA lowers have a HIGHER back sill, to prevent anyone from "dropping in" anything back there. The part of the upper that the pin pushes through will have to have meal removed from the bottom, or drill out the lower.

Or, just buy a quality upper from RRA and be done with it...
Link Posted: 8/13/2002 6:23:12 AM EST
Link Posted: 8/13/2002 4:43:11 PM EST
[Last Edit: 8/13/2002 5:06:08 PM EST by TheRedGoat]

it is not contacting the back sill.


It will go down about a 1/4 of the way (1/4 of the rear lug from the upper enters the lower). It gets too tight to force it into place.


Link Posted: 8/13/2002 5:03:03 PM EST
Goat, i had one to fit "tight" like that, all i did was file the rear lug of the upper. no big deal, you would be filing a little metal at a time with a common flat file.
now if you were going to "grind" it away with a hand held grinder, that would be cause for serious concern.
just my 2 cents.

Link Posted: 8/13/2002 5:18:08 PM EST
[Last Edit: 8/13/2002 5:30:10 PM EST by Kevin]
Link Posted: 8/13/2002 6:17:30 PM EST
I had an LEGP lower (RRA) with a BM upper. The two fit together beautifully and functioned perfectly. I now regret having sold it. If the right fit is what you're looking for, you might try sending both your upper and lower to RRA and have them match a lower to your upper. That is if, the suggestions above do not work for you.
Link Posted: 8/13/2002 7:02:30 PM EST
Suspect Kevin's on the right track. I do know that RR stuff is usually minimum tolerence, precisely so that their rifles don't rattle like a bucket of bolts when assembled. Of course, I can't know for sure without having the piece in front of me, but if the upper goes in even part way, I would strongly suspect that the rear lug on the upper and the side walls of the lower need a lttle "wearing in".
Link Posted: 8/14/2002 3:57:19 AM EST
I fixed it.

I lightly sanded away a very small amount of material from the Bushie upper. If you did not know to look, you would never see the modification.

It is super tight, and you do need to "slap" the buttstock to break it back open, but it is a very nice fit.

I am sure it will wear into place over time.

Thanks guys/gals.

It made it easier to remove the material knowing that I had a crack team of shadetree gunsmiths watching my back!
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