I would think that any bullet up to 260 grains or so will work well in a Henry Big Boy Brass or Steel at standard .45 Colt velocities. With the 1:16 twist, it should stabilize even heavier bullets well.
Henry Big Boys have a reputation for fine accuracy, and the one that I examined appeared to have deeper cut rifling than my Marlin .45 Colt 1894CB in .45 Colt. The deeper rifling and faster twist should increase accuracy.
The Marlin 1894C in .45 Colt has a slow 1:38 twist and seems to prefer the Federal/American Eagle 225 grain JSP load for accuracy, which isn't surprising when you consider that this twist was intended for the original .44-40 / 205 grain loading at around 1250 FPS. (Standard .45 Colt loads only run around 1100 FPS from a 20 inch barrel.)
Personally, I would stick with a standard JSP or JHP bullet for hunting with .45 Colt.
The FTX bullets seem to be all about spitzer bullet accuracy at higher velocities, which is exactly the opposite of what .45 Colt is all about.
For a plinking load, you would want cast lead bullets for economy.
AA#5 loads listed in Lyman 48th Reloading manual under .45 Colt rifle
225 grain JHP / 11.2 grains at 1170 FPS / 11.8 grains at 1258 FPS.
250 grain XTP/HP / 10.9 grains at 1124 FPS / 11.5 grains at 1217 FPS.
250 grain Lyman 452664 cast / 10.5 grains at 1133 FPS.
The AA#5 loads seem to be listed for every .45 Colt bullet type and weight, so I would think that it is a pretty versatile powder for this, but I have never used it. The burning rate chart lists it between HS-6 and UNIQUE, so it is in good company.
My preference is for Hodgdon UNIVERSAL, which is very similar to Alliant UNIQUE, which was and is the standard .45 Colt powder for many many years. But, I would think that AA#5 will work very well.
Last edited by saddlegun; 05/23/21.