Wasn't sure where to post this. I have a RRA receiver and LRPK and want to build an SBR. I thought it would be nice to use a RRA upper but they only have a 10.5" shorty. Wondering what the general opinion is to ideal, or shortest reliable length for an upper. I can't use a 7" in MD. and not sure I want to go as short as 10.5" either. I was thinking a 11or 12 would be better. So just looking for recommendations. I have a 10.5" ADCOR piston upper but do not think I have confidence in their future.. Should ad I also wan to use this on a Reg Receiver also, Colt M16. Thanks all.

I think 12.5 is the ideal AR barrel length.

I really like my 11.5.

http://www.ar15.com/forums/t_2_138/174764__Q__Why_BCM_chose_the_11_5_SBR_over_the_10_5_.html

This is the answer to your question.

Both are correct. I have a colt 6933 11.5" factory SBR and an ADCO 12.5" SBR. I really like them both. Both are dead reliable. The 11.5" is handier but the 12.5" seems to handle better. If I had to choose just one? 12.5" is the one.