Doug, did you get your Trapdoor yet?
If so, have fun ... I'm sure you love it.
You were interested in a light load earlier and asked about 45 Colt. As said already, DON'T try shooting one in your rifle. I have fired primer-powered 45 Colt WAX bullets (inside-the-garage practice shooting ONLY) but that is the ONLY type I'd bother with.
As you may know already, the Carbine load was a reduced load from the standard. They eventually had a load using a 405 gr. bullet or a 300-350 gr. (I don't remember exactly) powered by 55 grs. of BP, but that's as low as they got.
(On a side note, the Military NEVER officially bought ANY Winchester repeating rifles after the few Henrys purchased during the [un]Civil War. [POSSIBLY some for testing, but not issue.] Despite what you'll find from the "John Ford Reference Library." {Hollyweird} Any Winchesters used, and there WERE some, were privately purchased. I THINK that the first actual repeating rifle purchased by the Army - not sure about the Navy, or when they got their Lees - was the Krag-Jorgenson. Actual experts like Drydock, Pispitr, River City John can correct me here.)Back to the topic at hand. If you reload, there's nothing stopping you from buying some 200-250 gr. bullets (make sure they're sized from .457"-.460") and making a load using 40 grs. of BP WITH fillers or wads to make sure of NO airspace under the bullet and making your own Gallery load. BP is very forgiving that way ...
IF there is no airspace under the bullet!
I envy you - I've wanted one of those H&Rs or even the later Peder-Trapdoors for DECADES! (I saw my first H&R about 1972, and longed for one since then!) Unfortunately, my wife thought she needed a second dress or something frivolous like that, so no T-Door for me.
Have fun!