Please help here I have a fellow who just gave me a 44 Cal with a 3" Chamber shotgun the muzzle is .425 ID and the chamger fits a 303 British brass with the necked down area removed , He don't know what it is? and I don't have a clue ? has 1901 patent date on side , a break open single shot type made by H&R .My guess is that some one cut the rifling out and tried to make a shotgun ? Help Please !

Just a swag on my part, but it could have been origionaly chambered for the 44XL Shot cartridge and someone opened it up to use the 410 due to availability of ammunition. It would have been smoothbore from the start. If it is marked 44 than I would bet this is hte case. http://cartridgecollectors.org/410/collecting410.htm
has a good picture to compare the two cartridges.

Thank you Thaine !