I have one of these in a 20 Ga. W/3" chambers and 26" barrels. The serial no is B557XXX. It has what I think are proof marks on the barrels (SP8 followed by 22 on the right bbl. and SP8 followed by 5 on the left bbl. Does anyone know for sure what these marks are for? Also, when was it made and what do you think the chokes are? Thanks for your help!