I briefly owned an M1899 Sporter, in the correct s/n range (have Gene's book) which was marked ".236" ahead of the forend tip. I was told, but never verified during my brief ownership, that the rifle was chambered for the very rare .236 Remington, NOT the common 6mm Navy round. At this point I cannot verifiy anything, just thought I'd throw it out for comment. The rifle is probably still in Northern CA . . .