I have taken and been in on the taking of a few dozen moose here in Alaska in the last 50 years and they are not bullet proof at all. But, hit them in the wrong place in thick timber and fading light and they will move out of sight quickly if pushed. Most of the moose shot by me, my family, friends and most Alaskan moose hunters are taken under 100 yards. Most of them could easily have been taken with iron sights.
I would start with new Starline 45-70 brass, H322 powder and WLR primers. I put 54 grains of H322 in my Starline brass, I used to use 56 grains until I read the burn rate for H322 may have changed and Speer dropped the 56 grain load from their loading book. I started loading for the 45-70 in the very early 90's and found H322 to work wonderfully with 400-405 grain bullets, but the Swift, and defunct Alaska Bullet Works bonded bullets are plenty for moose, as would be the 350 grain Hornady or Speer.
North Fork, and Barnes, Woodleigh and others all make "boutique" 45-70 bullets. They are costly. We always try for a double lung shot and prefer a bullet that makes two holes. I suspect a 405 grain hard cast would be good at making two holes, but for lung shooting moose, I will stick with and expanding bullet at the expense of penetration.
Recoil with a case full of powder and a 405 grain bullet is no fun from the bench. So most of my range shooting with the 45-70 is done with the dreaded Led Sled, shooting sticks or standing with a tight sling. Long live the great 45-70!
