If bought used, with out dis assembly you will not know for certain.. WE (Only the factory has records to show.) cannot know by serial number alone.
Pull the butt off and see what the threaded end of the receiver looks like.
If its solid, its a SB2 if its not its a SB1.
CORRECTION: If its solid its a SB1 If not its a SB2.
Yes I know the difference,
Thanks for the PM's and comment Tim!
CW
EDIT, CR receivers are SB2 with case COLOR coating. It can come off and scratches fairly easily.
IMHO not a pretty as the early SB1 and PRE SB1 shotgun receivers. I liked the purples and reds that are lacking in the current colored receivers.
CW
EDIT to correct miss speak..err type.