I deer hunted this year with my Henry 45 Colt Xmodel with a suppressor. The Henry has a 1-16 twist so you can shoot 300 grain bullets. I took a doe at 20 yards with a 300 grain XTP going 1070 fps. There was full penetration and a good blood trail. It only went about 40 yards.
In my experience with penetration testing I would recommend a flatnose hard cast if shooting 250 grain as you want sufficient penetration. In 300 grain you can use an XTP or a hard cast flatnose.
The Speer 250 deep curl expands quickly and will not penetrate as deeply but it will hammer small game. It's also very accurate and will shoot one hole groups at 50 yards. The 230 XTP is another great small game round.
The advantage of the 45 Colt is having bullets that were designed to expand at subsonic velocities. The 300 grain XTP is about perfect for moderate expansion and deep penetration.
I did end up selling my .45-70 for the same Henry X in .45 Colt. I'm very happy with the decision to switch, as it feeds well, uses less powder, is quiet, and is lighter.
We carried it with 250gr this year (didn't get any close shot opportunities though) because I didn't have time to test a bunch of different loads in time for deer season. I'd read some chatter about the 300gr+ loads maybe being too long to feed in the Henry Big Boy action -- am glad to hear they worked for you so I'll try to get something worked up in the next year.
