Check these videos out (one of six):
https://www.youtube.com/watch?v=4WNYGs2_UZw
He also has one in which he shoots a Colt Army with various projectiles and standard Goex.
If you use Swiss, Olde Eynsford by Goex, or Triple 7 you can achieve some fairly powerful loads. If you use most any other powder you'll be pushing it to get 300 ft/lbs with it. But then a patched ball from a rifle kills deer just fine and often giving a complete passthrough at 100 yds or so, and it has about 300-400 ft/lbs at that point.
I'd prefer a bullet for hunting though, and one with a wide meplat. It's why I had this made:
http://accuratemolds.com/bullet_detail.php?bullet=45-195C-D.png
Note that at 195 grns it's only as long as a ball (.460") and has a very wide meplat. You can still get a full charge of powder behind it, and using Mr. Beliveau's testing in the ROA and using Triple 7 I'd imagine I can easily get 500 ft/lbs with it. But I found my accurate load is 35 grns in my Ruger and 30 grns in my Pietta Remington '58. I use 3F Triple 7 or Olde Eynsford powders and they both hit the same POI with the same favored charge and give the same size groups.
The Pietta frame had to be modified to load these bullets though.
The Walker was designed to kill a horse at 100 yds. It will certainly kill a deer at close range with that small rifle charge.
There's a fellow who hog hunts with his Walker and uses 2F Triple 7 with a ball. His friends, including Kaido, use Kaido's bullets (modified Lee 255 grn .45 Colt bullets). The Walker fellow claims a greater wound by the ball within 25 yds.