Elmer Keith once wrote of an old gent he knew who was among those who killed the last of the grizzlies in California.
He did it with a Colt Dragoon, according to Keith. No mention of load but Keith said the gentleman waited in a tree and shot the grizzly in the back of the head with the Dragoon.
I suspect he must have baited the bear somehow.
Does that mean you should go after grizzly with your Walker? Hell no! Not unless you want to be some grizzly's dinner.
The Lyman Black Powder Handbook (copyright 2001) lists up to 45 grs. of Pyrodex P (not actual grain weight, but equivalent to the volume occupied by 45 grs. of FFFG black powder) under a 140 gr., .454-inch ball.
This gets 1,038 feet per second (fps) at the muzzle for 335 foot pounds of muzzle energy. At 25 yards, that ball is down to 958 fps, for 286 foot pounds of energy.
Now, that's a rather piddling load by today's standards.
But with an ideal shot, at no more than 25 yards, I should think it would take a deer if you placed the bullet in the right place (head or neck).
I don't actually know that but I do know that millions of deer have been taken with far less.
I knew an old gent in northern Idaho who took deer with a .30 Carbine every year. He limited his shots to no more than about 50 yards and always hit them in the neck or head.
He waited in a tree, overlooking a game trail, and if he didn't get the ideal shot he simply didn't take it.
That man had discipline, extraordinaire.
You should be asking yourself, "Do I have the discipline to pass by shots that are not ideal? Do I have the discipline to practice with my Walker until I can put every shot into a 5" inch circle, offhand, at 25 yards?"
Therein lies the rub.
Using the right caliber is part of it. But much of it is the integrity to pass shots by that might result in wounding or loss game, and to dilligently practice.
Yes, the Walker will take deer. But bear in mind that it generates about the same or less energy as the .45 Auto, 230 gr. roundnosed lead bullet.
However, soft lead balls tend to flatten when encountering resistance. For this reason, they tend to offer "killing power" all out of proportion to the size and weight, and outside the realm of mathematical formulas.
A case in point is the .36 Colt Navy, which had a fiersome reputation as a mankiller. But looking at that little lead 80 gr. ball, you wouldn't know it.
Yes, you can use some kind of conical bullet in your Walker but it's at the expense of powder, and that lowers your velocity.
Also, in my experience, conical bullets lack the accuracy of the round ball.
Whoever said the Walker repro is a wall-hanger is wrong. It can be a powerful handgun, if well-made. Trouble is, there are some poorly made repros out there and some damned fine ones. I don't know what you have. If you can get it to put all six balls into a 3 or 4 inch circle at 25 yards from a benchrest, you have a good one.
The Walker, like all Colt percussion guns, is hampered by its rather crude sights. A brass bead up front and a notch in the hammer for a rear sight. Neither are adjustable.
And every Colt, old and new, shoots high. Some as much as 12 inches high at 25 yards with a full load. To counteract this, you have to add a taller front sight and/or file the sighting notch in the hammer slightly deeper.
Getting a Colt percussion to shoot to point of aim is a challenging task but can be done.
Once done, a well-made percussion pistol can amaze you with its accuracy.
But you have to work at finding an accurate load.
You've got a big task ahead of you. But if you spend this spring and summer at finding an accurate load, then practice with it, you could take a deer with a neck or head-shot from 25 yards with that Walker.