A magnum bolt head, a barrel and some tweaking of the mag.
I looked at it but the single source of brass and the fact that the cartridge doesn't look like it is going to make it turned me off.
Then looked at the shortened 458 mag but you either have to inside ream the brass (yuck) or form 350 Rem brass (easier but still...).
Ended up with a Siamese Mauser in 45-70. Thinking about a Dane Krag in 45-70 too...
Bookmarks