I recently traded locally for a Colt SP1 lower, upper and BCG, it was missing the barrel assy and has a A2 buttstock/grip. It is a a SP177XXX serial number, is this from the last year of SP1 production before the sporter II markings came along? I'm pretty sure the buttstock assembly and grip is not original, the previous owner claimed to be the second owner and bought it back before the ban that way and never did anything with it till I got it from him. The BCG is marked with the usual "C/MPC" markings and the upper is a large hole slickslide and they are a close match in color, a slightly dark grayish color. I'm assuming this may have been a carbine and the buttstock and barrel were removed and sold due to the value on those parts, especially the buttstock, it should have been the 2-position vinyl acetate version usually installed on the SP1's. Any of the Colt experts have any potential info on this, I think I came out ahead as I traded one of those complete Brownells Colt lower assemblies that could be registered as a pistol for this.