One of the things I have been trying to do, which I did not do last time s determine the frame size on this 10 gauge. Seems like it could be a 3 or a 4. The width of the receiver seems small for this gun. This is an early gun so there is not a frame size on the lug. Here are some key measurements.

Width of barrels at breach - 2.48"

Distance between firing pins - 1 1/4"

Distance between bolsters wasn't sure of the best measurement on this. At the furthest most point between raised sculped edges it's 2 5/8" right at the breach next to the barrels it the same as the barrels at 2.48"

Distance across hinge Pin - 1 5/8"

Standing breach height - 1 3/8"

It seems like aspects of 3 and 4 frames sizes though the barrels are slightly narrower at the breach than my #4 frame top action parker from 1886. Since this is an early gun it might not have been standardized yet.