A C&B Revolver is quite capable of taking Deer size game at reasonable "40 yards or less" range but the weapon & person has to be in unison when taking on the challenge of hunting Game with a C&B Revolver.
Loads should be on the heavy side to achieve the most effective energy required to take these larger game & ofcorse practice, practice, & more practice is in order for the person to know what he/she & their weapon is capable of at those maximum distances.
Round ball is the most popular projectile with a charge of 35+ grains of powder would produce very positive results but a good conical like the ones cast from Lee's molds "of Pure Lead" with a charge of 28+ grains of powder will produce a slightly heavier striking energy than a Ball would but like mykeal mentioned they do not expand as much as a ball would.
With this information, the person has to have a little more patience, & reservation like an Archer to wait for the closest shots so that a clean Killing shot is possible, I hunt with Archery gear mostly with only on occasion with my Muzzle Loader & for over 25 years I have followed a simple but effective rule in taking game with my Bow & would be a good one for the Black Powder Pistol hunter.
20 Yard Rule.
I can keep my broad heads in a 3" group nearly all day at 60 yards at the target range.
I refuse to try a shot at any animal past 40 yards.
I know that my Archery gear & I am very capable of taking even Elk out at the 60 yard range but in the woods there are variables that cannot be controlled like can be at the target range & lessening the range by 20 yards will give me the confidence & the know that I can cleanly take an animal with no regrets of me making that bad shot that I could have avoided.
Following a similar rule in Black Powder Pistol hunting will not only make you a more ethical & responsible hunter but will also make the hunt that much more satisfying that you got that close to your quarry.