Hi everyone, newbie ar builder here, I am trying to decide which upper to use,I know I want a 16" flat top for the versatility, but what if any are the differences in the m4 and regular car other than barrel profile and fore grip size? also what about the dissipator? I thought I read somewhere that it will not  accept a bayonet.Also is there much of a weight variation,balance etc. between these? Thanks for any and all replies.

anyone??????????????????????

Welcome! Best advice I can give... Find a shop that has a few in stock, handle 'em and see for yourself. That is the way I have always done things and I am very happy with the decisions Ive made. Not sure about your dissipator question, but if its a Post Ban upper it will not allow a bayo, as I am sure you know. If you have a range where you are see if you can try a few rounds W/ different ARs and build the one you like best. If you change your mind, build another. I am on my third and proud to be an AR junkie.. John