I had some problems reducing the load for the Henry from what I used for the Ruger Redhawk and the H&R Colt Carbine. Full pressure load for the Max load was H110 at 26 grains under a 250 FTX or 240 XTP Mag. 1450 ft/sec from the Ruger and 1750 from the H&R. This load may damage a Henry. Reducing loads with H110 is not advised from the Hodgdon information. I went with Unigue and RL7 got the speed I needed for the Henry about 1000 ft/sec, very dirty, soot all over the cases. Same sooting you see with cowboy loads. Looking for something better I tried Trail Boss, a very different powder, looks like little washers and is made to nearly fill the case and used by the cowboy shooters. I shoot 9 grains under a 250 XTP bullet at 1.600 length, getting 1025 ft/sec ot of the Big Boy 45 Colt. To shoot the 225 FTX the cases need to be shortened to 1.215, this info came from Hornady on an email request for load data for the 225 FTX to get the OAL 1.645, short enough to feed in the lever actions. Note 240 XTP grain Mag is for 454 Casuall speeds, 250 XTP is for slower speeds and the 225 FTX is for the 1000-1100 speed for the Henry, see Hornady Lever evolution load data, 250FTX is for the 450 bushmaster at 2200 ft/sec and may not expand completelt at 45 colt speeds. I also have a 450 Ar-15 upper and it is a very accurate load. Use the Trailboss and the 250 XTp or 225 FTX and you will see an accurate and clean load for the Henry Big boy.
Here is the Hornady link, info now on their site:
http://www.hornady.com/assets/files/ftx_load_data/45ColtFTXRifle.pdf