Will my NEF handi rifle 45-70 handle heavy loads?
Yes! The .45/70 NEF's will handle the same loads as a Ruger #1 or Siamese Mauser, altho most .45/70 shooters I'm aware of usually limit their loads to those for the lever-guns, to better enjoy their guns and manage substantial recoil.
I don't yet have a .45/70 barrel for my NEF SB2 Handi in .308W, but I do have the .280R and a .444M is on its way to me.
NEF/ H&R .45/70's will handle the stoutest .45/70+P ammo from Cor-Bon, Buffalo Bore or similar makes.