I was looking at the ARMS catalog and it mentioned in a disclaimer that they only warranty and guarantee Bushmaster Armalite and  Colt , I know I have seen them on RRA in AR15.com - I have haven't I ?? A Sir System  will fit on a RRA - correct ???      

Thanks I have some money burning a hole in my pocket and would be my luck that it would be just a Nth off and wouldn't fit .ARMS never stated that it wouldn't fit RRA just that they dont warranty or guarantee except for those brands I mentioned . - Your right they should at least be specific, they must not know how passionate we are about our urban defense units !

DPMS and RRA have put out some uppers with out of spec rails in the past.  Thus the disclaimer.

Devl is right, RRA were saying they had the only correct recevers, but that was a BS answer and finely admitted the problem and took steps to correct. DPMS on the other hand, well you never know what source they get thier parts from, hence the receivers have been a problem to many on this sight from what I have read.
Good Shootin, Jack

I have placed SIR's on DPMS uppers with no troubles but...

I have 2 SIRs, a #45C on a DPMS upper with M4 profile barrel, and a #58M Bi-level on a RRA Mid-Length upper.  The only problem I've had was with the #45C, if you can believe that.  They didn't machine part of it correctly, and so it wouldn't slide all the way on.  Upon close inspection, you could tell where they had screwed up, so I just took a file to it and relieved about 1/32 of an inch from the underneath of one side.  I know most of you are thinking that it's the upper that was out of spec, but if you had seen what I'm describing, you'd believe me.  I'm sure that ARMS would have replaced it for me, but it took less than 5 minutes to fix with a file.

Nope, the #45 etc. are machined very close to fit the mil spec dovetail at the front inside for about an 1/8 inch. If it did not go onto that after market receiver for that last 1/8 inch, the receiver was not to the militaty dimentions, the SIR was not the problem.
Good shootin, Jack