This is not necessarily going to hurt accuracy? Yeah you are right, try to see the good in everything, it gives me a little extra space for more powder. Those 520 grain bullets need a good push anyway.
Though keeping the exposed grease groove clean and the soft lube in place is a bit of a PITA, just wiping off the excessive lube after seating the bullet and everything is gone.
45-90? That was my first thought, but there is clearly a .45-70 stamped onto the barrel. Whats a good way to measure the chamber length?
Oh, and is it possible that the bullets are simply too small ( .457 & .458) so they crawl deeper into the barrel than a .460?