Wander over to the NEF/H&R forum. This conversation has been repeated ad nauseum.
That's right, it comes up over there once a month or so. I already said that I have commented on that particular
subject on that forum for the last time unless I decide to on an existing thread. A man has to wash his hands of the matter at some point.
Remember the diff in dia. of bolt/thrust, let the folks over there tell you about that, complete with charts, what you can do with a 30-06 case does not translate to what you can do with the 45/70 case.
Some feel that you can load to what the case can stand before you have a problem with the Handi when it comes to the 45/70. I don't load in that fashion when it comes to the 45/70.
Some will tell you that you can use Ruger Number 1 data, but I sure won't & I don't think you will find the major loading manuals to load the Handi with the data for the MUCH stronger Number 1 either.
I believe the primary Loading manual foks will put the Handi in the Marlin catagory, I trust their judgement over home brewers without all the pressure testing instruments at their disposal.
The nice thing is the Marlin levels will do fine for all NA game.
One thing for sure is plent of Handi enthusiasts will tell you what you desire to hear but I would use caution. If it's really important to you, contact Speer, Sierra etc.