The more you have to build your story up, the less credibility you have, there is no way in HELL that you got 2270 with a 400 gr bullet, that is near 416 Rem mag velocities with the same bullet weight, are you saying that you can duplicate this with the senile 45-70? Don't get me wrong, the 45-70 is a great cartridge, but, you did not get 2270 FPS, I dont care if you used a 32" barrel with 70.0 grains of powder, you didn't achieve that velocity, and you know it.
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Gee, HOG! I have low credibility with you, eh? Now, THAT's truly a problem!!

FYI, the load I USED was 60 grains of HERCULES RE 7 powder, Remington cases, Barnes Original 400-grain semispitzer bullets, and Federal 210 primers. Now, that powder is gone. I have no idea if the current Alliant RE 7 is anywhere near the same, as I have not tried it yet, and don't need to,since I still have around 60 rounds of that old load left. But I have heard it is FASTER. If so, 60 grains of it might be too much.

BTW, the .416 Rem., and the .416 Rigby, both have almost2400 FPS with the factory 400-grain bullets. But it is a little easier to get comparable velocities with a 400-grain .458 bullet, because it has lower inertia. The ONLY limiting factor on higher velocities in a 45/70 is the limited POWDER SPACE.