I need to find out what cartridge was used in this extremely rugged line throwing gun, probably naval rather than commercial use. Cartridge is probably similar to .45-70 as it is a rimmed case. I cannot do a chamber cast yet, but looks like rim diameter will be .650" - .700’ and the bore diameter is about .445". This fires a very heavy projectile weighing 880 grams or a little over 1 pound 15 ounces. The projectile is a solid steel rod which fits into the bore about 15 inches, with a steel head with a shroud that slips over the outside of the barrel for about 6 inches. This does not appear to be any sort of whaling projectile, but strictly for line throwing purposes. The extreme weight of the projectile justifies the overly thick stock and massive steel buttplate intended to be placed against a solid structure, not shoulder fired.
It was supposed to be a souvenir brought to the U.S. after WW2.
Any help on identifying the cartridge would be appreciated. And, any info about the model designation for the gun itself would also be appreciated. The action is similar to a Type 38 or Type 99 but purpose built with a solid receiver bottom, not cut for a magazine.
I apologize for the lousy photos, but they at least give an idea of what the gun looks like.