The MagTech 2-7/16" shells should duplicate the 2,5" shells that the 1887 was constructed for pretty closely.
Back in the day the 2,5" all-brass shells would have been roll crimped too.
I have an early-production Norinco 1887 chambered in 12/70. I use un-cut, un-crimped MagTech all-brass shells, but do not load them from the magazine; I put one in the chamber and one down on the cartridge lift. I have done some smoothing of rough edges inside the receiver / chamber area, and this set-up has served me well for years in CAS-mainmatch.
I will have to do some more experimenting with paper or plastic shells in order to make it feed six shells from the magazine for Wild Bunch.