Keep in mind that when considering a cartridge, there are three separate ballistics to consider; internal, external, and terminal.
Internal ballistics involve what happens between the time the primer is popped 'till the bullet leaves the barrel. Powder burn rates, barrel harmonics, and such are involved.
Exterior ballistics involve the trajectory of the bullet from the time it leaves the barrel 'till it hits the target or backstop. This is where you'll find more difference between cartridges.
Terminal ballistics involve what happens as the bullet passes through living tissue. In truth, there is no such thing as "knockdown power", or "stopping power". If the living target is stopped, it's a function of the terminal ballistics of the cartridge/bullet/load combination.
Tables, mathmatical figures, and such can give you some idea of what to expect from a given cartridge, but there are flaws in all of them. They tend to not consider bullet placement, and can't compensate for the stamina and resilience of an individual animal.
There are energy/momentum/KO calculators available online, and a quick search will provide several of them. When considering the capabilities of any given, unknown cartridge, I tend to take all three of these into consideration.
I like the Taylor KO formula, but it tends to favor bigger, slower bullets. I've seen too many animals killed quickly by very light, fast moving bullets to discount them. That's the flaw in that formula.
Energy figures are the opposite; they tend to favor light, fast bullets over heavy, slow ones. Again, I've seen some heavy bullets kill game very quickly, and penetrate deeper than most would expect. That's the flaw in energy figures.
Momentum will give you more information, but it's not a reliable factor in and of itself, since a thrown baseball has a lot of momentum.
But when you take all three into consideration, you start to get an idea of what to expect from the cartridge when experienced advice is unavailable.