All I've ever heard my entire life is "you can't shoot full power loads in a trap door, because the action is too weak". Is that hogwash, truth, or is the truth somewhere in between?
This is truth, but moreso somewhere in between. Depends what you consider "full power."
The Lyman 49 manual seperates .45-70 loads into three categories - Springfield Trapdoor, 1886/1895 lever guns, and Ruger No1 or No3 loads. If you compare the 405-500 grain cast bullet starting and max loads on the Trapdoor and lever gun loads, you'll see some near overlap. Essentially a Trapdoor max load is a starting load for the lever gun-level loads.
The H&R break action rifles have been rated to match the lever gun level loads according to all the reputable sources I have read. I regularly use 35.0 grains of 4198 under a 405gr cast bullet in my H&R's, which Lyman 49 lists as a max load for the Trapdoor (listed at 1463 FPS out of a 24" or 30" barrel; not sure which). While I'm not a hunter, I'm not sure I'd ever need more power than this for anything that walks or crawls on the North American continent. If you want to load hotter than that, the H&R gives you a lot of room to do so.
I can't say anything bad about the H&R's I've owned. They are a lot of rifle for the money. Very affordable and handy. The break-action design also makes for a very short action, making it very compact and well, again... handy. You could also buy 2 or 3 H&R's for the price of 1 Trapdoor. And if you're lugging it around for hunting, you might not feel as bad about getting little dings or scuffs on it as you might on a nice Trapdoor. Food for thought.
For more info on the H&R's, I'd suggest checking out the NEF/H&R forums over at
Greybeard Outdoors. There's a lot of GREAT information collected there in their
FAQ section.
I'll add that I would REALLY love to see a manufacturer like Rossi come along and make an affordable Trapdoor or Falling Block replica. Just hasn't happened yet.
I just ordered another .45-70 handi that should be here later this week. A 18.75" carbine:
I also previously owned one of the .45-70 Buffalo Classics, which I had really good results with, and sort of regret selling.
Good luck.