Does anyone know where I might find information on the serial numbers for the  Colt SP1 Carbines. I bought an SP1 at a gun show and it was dressed with the A1-16" upper, and the metal 2 position collapsable stock. But I want to know for sure if I got a good deal on a true Carbine, or just something someone put together.....

Try here for variants: www.biggerhammer.net/ar15/variants/ and the serial number list is up top under Articles/Legal at the bottom.

Mike

If it actually has an A1 upper, with the forward assist, then it's not totally original.  The SP1s never had the forward assist.  If, on the other hand, it has the smooth side upper, then it probably is original.

I don't know if Colt kept any records on which SP1s went out with 16" rather than 20" barrels, but you could check w/them. Unfortunately, all the SP1's went out with the same reciever markings.