I have a load using a Montana Bullet Works hardcast with a gas check. Can't remember for sure but I think it's 405gr at .458". I was driving those pretty fast.
I've got some of those as well... they are fantastic bullets, just expensive.
Midland, you are driving those bullets too fast. I have data in my notes from when I had my Marlin 1895...
With the 405grn Montana gas checked bullet, 47grn IMR3031 gave me 1720fps, 47grn IMR4895 gave me 1525fps, 48grn IMR4064 gave me 1650fps... all those were brutal on the buttstock and I wound up pulling almost 100 cartridges. Even with the gas checks, the accuracy was not good, and I was getting indications of leading at the barrel muzzle, too. That same bullet, with a more sedate charge of IMR4198, gave me 1270fps and 1475fps (30 and 35grn IMR4198, respectively...) and far better accuracy. Further, I didn't have to send out a search party for my retinas, and I didn't have to scrub the bore like a madman after 50 rounds of it.
In the .45-70, I've gotten completely away from slower powders and high velocity... there is no arguing with the physical laws of a 405grn bullet traveling at ~1300fps. I've probably mentioned this in a previous post, but IMR4198 is my cast bullet rifle powder. In the .45-70, you can substitute 2400 with good results, too...
I am working with some home cast (by a friend, I don't cast...) 385grn RN coated bullet. I don't know the hardness, but I would guess they are in the 12-14 BHN range, and he's coated them with some snotty, sticky stuff. 18grn 2400 puts me right at 1200fps with very good accuracy, 28grn IMR4198 gives me right at 1350fps and excellent accuracy. I would have no problem poking piggies with either of those loads.