Those original blackpowder .45-70's used heavy bullets - very commonly 405 grain lead - and pushed to a modest 1200 fps or so.
Original early load for the .45/70 was a 405 grain bullet. The later "infantry rifle" load was a 500 grain RN bullet, at a bit lower velocity, thus .45/70/500. The 405 grain load was downloaded a bit for carbine use, and ended up as the .45/55/405.
Thank you for the sensible responses regarding my question on hard cast projectiles. Using hard cast projectiles in rifles is a new thing for me. My original intention was for plinking as the Marlin has Ballard rifling.
If you have ballard type rifleing, why all the worry about "hard cast" bullets? You should be able to get 1800 FPS easily with the correct bullet diameter and lube, along with a gas check. hard bullets tend to fragmnent, softer bullets will hold together and still penetrate well. IME, people worry way to much about bullet hardness!
Seeing the length of ploughed up soil made me think these 405gn slugs could possibly be good on a pig. Hence why I asked the question.
There isn't a pig alive that your 405 grain bullet won't put down, assuming any sort of decent hit. If you can head shoot rabbits, go shoot some pigs and find out for yourself.
For those who worry about the Microgroove curse, while you are flogging around the Beartooth Bullet site, read Marshall's tech notes on the .444 Marlin. Cast bullets will work well in multigroove barrels if you do a bit of research. Bullet diameter is much more important than hardness, IME.