Generally speaking, the Remington Arms Co. doubles in 12-gauge had 2 5/8 inch chambers. On the Remington Hammerless Doubles, if they were ordered for a longer shell, the chamber length was stamped on the bottom of the barrel tubes just forward of the barrel flats. I've never seen a Remington Hammer Double marked for a longer shell. Here is a hang-tag for a Remington Hammer Double of 1902 vintage --