I know this is the "Lever Action" forum, but it also seems to have a lot of 45-70 posts (and the Marlin site is now gone). I recently purchased a Gibbs 45-70 bolt action rifle built on a Enfield #4 mark I action. (This was my first non-lever action rifle and I rationalized it because of its resemblance to the Lee-Remington 45-70 of the 1879-1899, but I digress...). I had a local small commercial handloader who I have used for years make some ammo for me and we were surprized to discover that it could easily handle a Hornaday 500 jacketed soft point at the crimp for a overal length of about 2.9 inches. I should point out that Gibbs is now advertizing rifles built on the Enfield #1 mark III action, so they could be different. Mine has a barrel marked "Navy Arms" and is 22". Even though both Gibbs and the British Army converted #4 mark I to 308 Winchester / 7.62 NATO, I had him keep the 500 gr (at 2.9") down to about 1,600 fps.