44 caliber cap & ball revolver loaded with a 140-grain round ball over 30-grains of 3Fg Goex black powder only generates 242 ft/lbs of energy. In comparison, a 124-grain, 9mm round produces 304 ft/lbs of power.
Based on that, when we are looking at cap & ball revolvers, we should ensure that they hit with at least the power of a .380. If we look at a .380 round that pushes a 90-grain bullet at 1,000 feet per second, we'll see that it develops 200 foot/pounds of energy. So, if we are going to depend on a cap and ball revolver to save our lives, it needs to hit with at least 200 ft/lbs of energy. And that is the power floor set by both sets of researchers for a reliable self-defense round.
The fact is, loaded with an 80-grain round ball and 22 grains of 3Fg Goex black powder, the .36 caliber Navy only generates 166 ft/lbs of power. To get close to the .380 power floor, you need to load it with a 150-grain conical bullet over 18 grains of black powder, and even that load only hits with 198 ft/lbs. But, as Marshall and Sanow discovered, bullet performance is at least as important as power. Cap and ball conical bullets tend to drill right through a body. That over-penetration means the bullet leaves most of its energy in the wall behind your assailant instead of in his body. For that reason, I recommend you only use .44 caliber revolvers for self-defense.