You would do well to keep to the 300gr lead load that the original shot. I have no experience shooting game with one here in UK, where it does not meet the government requirements for either muzzle velocity or energy [funny, that...].
So it IS proofed for the jacketed stuff you are using in it, but it seems more in keeping to use the original 60gr of BP 300gr load - somewhat kinder to the shoulder, too.
My .45-70 load in a Uberti High Wall is just 34gr of H4198 - not unpleasant and plenty accurate out to the maximum I shoot it of 200m.
And for Mr Kcivezleb - does your H&R Trapdoor have the modified latch? Originals from H&R had part of the breech block latch held on with a short screw - it was susceptible to opening on firing as the screw broke...the fix was to make the latch in one piece, like the real thing had been.