My Portuguese Kropatschek is a restored military but with the same deep grooves, about the same land & groove measurements, and gives the same sort of accuracy.  It will usually keep most of them in a paper plate at 100 yards.  I had a bullet mould that cast .328, but once I loaded the fat bullets in the cases (8x60R, made from .348 Winchesters) I could not get them to chamber.  Best luck I had was with bullets from a box marked "for 8mm Remington Magnum".  They were made by one of the regular bullet makers, maybe even Remington, and they were heavy, maybe 225 grains.  Those would all stay in the paper plate at 100.

I think the deep grooves are from early theory on how to make a barrel for a smokeless powder military rifle shooting jacketed bullets.  I think the deep grooves were intended as a place to store powder fouling while continuing to shoot, and also to allow some semblance of accuracy while the barrel was worn away from shooting a few thousand rounds. 

The issue bullets for the Kropatschek are steel, maybe plated with  cupro-nickle.  They probably caused a lot of bore wear.  The issue 8x60R loads were compressed BP. 

Could you get that Remington to shoot accurately? If it were mine, I would find some tapered soft lead alloy bullets intended for a 32-40 or .33-40 single shot target rifle.  Lubricate them with something like SPG. Breech-seat them in the barrel just ahead of the chamber.  Use a fired case with a dowel in the case mouth as a tool to push the bullet into place.  Then try a mild load of fast smokeless.  Maybe 15 grains of 4227.  The only wad should be at the neck, to prevent the powder from spilling out.