For my first ever AR. I am building one from the lower up. I have a RRA stripped lower. It wasn't my first choice but... I'm going to be building around it. I have a RRA LPK and two stage trigger on the way. My question is. Color match aside does anyone foresee any problems with a BCM 16" M4 upper not fitting properly? I have been reading different stories lately about quality being put to the side over quantity (I am not implying issues with BCM). If it is going to be an issue. I will be going a different route with a upper. Does anyone have pics of a RRA lower w/ BCM upper? Thanks

I have a setup like you're describing.  16" BCM M4 on a RRA lower.  Aside from some differences with the finish color, they work great together.

Link to pic (321KB):
BCM M4 Upper on RRA Lower (1024x728)