I've had a Damascus barreled shotgun before. This one appears to be a twist and not Damascus.

I took it out into the bright sunshine to look for anymore markings. The only thing I saw was Patd. 20.80. There were no marking as to gauge or anything.it's a huge bore, I'm at 12 or 10 ga. it's so big.

The link is the best thing I could find for information as to serial numbers. In order to get into the 10000 range it shows they changed their numbering system in 1919 and that is where the serial number seems to fit. If you look at numbers prior to 1919 they have designations of the different types of guns. I could not find a 10000 series of numbers for Hammer guns prior to 1919. So it looks like it might have been made in 1919.

Who the hell knows. Since it's going to go to the live bro-in-law, I suppose past the raw curiosity, I don't care.

I wonder if I should caution the b-i-law not to shoot modern shells in it or just let him find out on his own. dumb ass. hahaha