I've been doing some more digging on these rifles, apparently while they were really popular in South America, particularly Argentina, Mexico, and a few other places, these exact rifles were used in the Philippines during the Insurrection by the Moros in .43 Spanish.
It's hard to say where this gun came from, there are no markings on it from any nation, no stampings, other than inspection markings, nothing, not even a serial number. Only numbers are three on the buttstock, one going horizontal, a "2", and then a vertical "42". That and a "u" on each barrel band, nothing more. I don't think this gun ever saw service in any military, and after reading up on it in Mike Venturino's "Shooting Buffalo Rifles of the Old West", he wrote that these guns were sold like this commercially. I think that's what this might be. The bore looks too good to have been issued, many of these things have pitting and rust, this doesn't.
Here are some of the rolling blocks in the hands of the Moros.
