IMO the Remington bullet was designed to expand at Trapdoor velocities, or so I was told by a Remington rep quite a few years ago. It may stick together at higher velocities, I have shot a few deer with the bullets, but have never recovered the bullet. The bullet did knock them flat.
Personally I like the larger 405 grain bullet at about 1500-1600 fps. I also like the lead cast bullet-I prefer to cast them myself. I find that I get great expansion with this bullet, and it certainly knocks them flat. This load is not a shoulder buster. No added weight should be necessary.
IMO the 300 grain bullet in the 45-70 is a high velocity bullet(for the 45-70), and I would prefer a hard cast for that instead of the Remington. Tom.