Sorry I didn't catch this earlier, but the bronze tube is a repro also. The fort must have the original tube in some secure location, or it was stolen and they are displaying a repro replacement. How do I know it is a repro?
The boring of the bore does not have the appearance of an original bore.
The muzzle markings are made with poorly-aligned modern metal stamps and are not the proper wider-cavity lettering, perfectly aligned, that . I expect to see in original markings.
Alger 12-pdr. mountain howitzer no. 316 was inspected by Thomas J. Rodman (TJR) NOT "NPS" (National Park Service) as marked on the repro.
The maker's initials should be "C.A. & Co." I think, but maybe "C.A. Co." was used as well.