I love my SP1 Carbine. Mine will shoot 1.5 MOA using 55gr M193. I have a factory original SP1 Carbine in the 140xxx range. It has an A1 birdcage, 2 position coated aluminum stock, staked and marked buffer tube, upper is marked CM on the carrying handle.
I have a Chrome Bolt, Chrome Carrier(older style without the cuts around the firing pin), Chrome Chamber, and Chrome Bore. Seems the Chrome shop at Colt was busy at one time. One thing I have noticed the the variety of carrier/bolt combinations on SP1's (some green, some Chrome, even a green notched carrier in a SP1, ect...)
Here is a great link to help you out. Everything you wanted to know with pics!