If I were going to hunt deer with any ML pistol, I would want my gun to shoot conicals, and not round balls, to give me added weight in the projectile, and then I would want a barrel as long as I could practically use, so that it would burn up the most powder I could in that caliber. A .54 or .62 caliber with a 12 inch barrel would be my preference, so that the bullet would drive deep into the deer. Even then, the shot would probably be limited to 25 yards. Pistol velocities rarely get above 800 fps at the muzzle with any ML handgun. A .50 Ca. round ball only weighs about 180 grains, the size of a .357 semi-wadcutter, without all the impact advantages of that bullet. A .357 can be driven at 1200 fps. whereas a .50 cal. round ball out of a single barrel pistol will rarely exceed half of that velocity, without that longer barrel I mentioned. Weight of the bullet is what determines depth of penetration, but velocity certainly contributes to the process, at the bottom end. I have seen round balls bounce off the knots in railroad ties we used for a backstop in a range, when shot from a handgun, no matter how much powder we stuffed down the barrel. This from a .45 and .50 cal. pistol. As a result, we decided for safety sakes, and to protect our club from lawsuits, to not allow our pistol owners to fire their guns at our make-shift ranges where we did public demonstrations. RR ties were the most common material available in many towns to build a backstop, and it was just too dangerous to let pistols be used.
For small game, I think any pistol, with round ball will prove adequate. So, build the pistol, and have fun. :thumbsup: