Biggus

That's an awesome gun you've put together. Aimpoint 3000? You're quite right that Colt did refer to them as Model 653, Model 727 and so on, but not M653, which implies type designation.

The 653 was the R653 up to the adoption of the RO series of designations, which happened in the 1980s, 1986-87 IIRC. It was poor form of me to refer to it as RO653, as the vast majority were certainly produced as R653. Still, there is no such thing as M653, and I'd be very leery to see an M-series designator applied to anything that hasn't been issued one.

I think you mean 653. Specifically RO653. No such thing as M653, M727, M723, etc. They're not M-designated, even though there are NSNs for parts, uppers and whole rifles. The barrel profile does look a bit strange. It looks like a very heavy profile. I agree that apart from that, it's pretty close to an RO727. There are rumours of a very small production run of pencil profiled 727s early on, but I've never seen them. Contrast that with the 723, where plenty of them have pencil profiles and a pretty large number have the slightly odd pre-M4 profile with the M203 step down. 653s were ce