Ar 15 Id

How can I tell if my ar 15 is original ? My lower is marked Colt H bar sporter . Im not sure the upper is original to the lower. The color and finish matches but I noticed that on the barrel in front of the front sight it is marked B MP 1in 9 twist instead of C MP 1 in 7 twist that I normally see on Colts. There is a CM marking on the upper rt side of the carry handle. Also the barrel is thinner where it runs under the hand guards. I thought H Bar barrels were supposed to be thick all the way through. Any help with this? Thanks in advance

Unless you have a True H-BAR (complete heavy barrel) most H-BARS are thinner under the hand gaurds this is to fit the 203 grenade launcher.
I am not sure about your markins.
My Heavy Barrel is marked C MP 5.56 NATO 1 / 7 H B A R