My double rifle arrived yesterday. Did a chamber cast and it looks like it's a .450/.400 2 3/8" bpe. I've been told by a few folks that the 10.3mmx60R is the same cartridge. I went to this site, ( http://www.henrykrank.com/section%203%20Bertram%20Cases%20reduced.pdf ),and compared drawings of both cases. They do not look the same to me. I am trying to find the dies, brass and bullets. The 10.3 is much cheaper on brass and dies than the 450/400 but if they aren't the same it would be a waste of money. Can anyone say for sure that the two cartridges are one and the same?