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Posted: 1/2/2006 8:43:59 AM EDT
I have a Bushmaster 20" A2 upper that I am trying to put on a Rock River A2 lower.

I can push the front pin in, but I can not push the rear pin in.

It looks like if I give the upper a good wack with a rubber mallet it might fit.

So before I wack/force it, I thought I would ask

Is there a compatibility issue between Bushmaster and Rock River?

Link Posted: 1/2/2006 8:48:57 AM EDT
There is a factoid on the RB Precision site that states that RRA uppers are difficult to mate with other lowers...that the fit is very tight. RB has suggestions on the proper way to this. Suggest you visit their site...
Link Posted: 1/2/2006 8:50:44 AM EDT

Originally Posted By BrianB2:
There is a factoid on the RB Precision site that states that RRA uppers are difficult to mate with other lowers...that the fit is very tight. RB has suggestions on the proper way to this. Suggest you visit their site...



agreed....however many of the gang here has done the "whack n' fit" with success. YMMV...
Link Posted: 1/2/2006 8:53:50 AM EDT
If you got the rear takedown lug of the BM to fit into the RRA, it sounds like you're most of the way there. I suggest you remove the rear pin before you put them together and eyeball the clearance through the receiver. And yes, BM and RRA do machine the rear lugs and the receiver space differently.
Link Posted: 1/2/2006 9:00:03 AM EDT
I also have a BM DCM upper that won't fit in either my RRA or my Stag lower. However, all of my other uppers fit. It seems that BM cuts their rear lug differently and they are a little larger than the rest.
Link Posted: 1/2/2006 9:12:33 AM EDT
Ok, I will use some grease, and slowly work them together like RB Precision suggested.

Then wack it.

Thanks for the info guys.

Link Posted: 1/2/2006 10:07:13 AM EDT
I think there is some agreement among many here (including me) that rra machines their lowers a bit more narrow around the rear take down lug. I used the grease and whack method to get a dpms upper to fit rather easily but my bushy upper took a a lot more.

Good luck
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