Handgun self-defence rounds are tricky to select, but the same also applies to hunting rounds. There are a wealth of calibres available and a range of bullets. Comparing them is not easy- bullet weight, calibre, velocity and muzzle energy all have an effect on performance- but so too does the bullet design. Expanding hollow points are not always the most effective option and hard cast lead bullets can offer devastating penetration and bone-breaking punch. There have been various attempts at coming up with a reliable way of comparing various rounds and one of the most long-standing is the Taylor Knock Out- bullet weight multiplied by velocity and bore diameter and divides the result by 7000 (no. of grains in 1lb). It's not the most scientific method and the TKO has plenty of critics, but when you're confronted by so many different calibres and cartridges, the TKO can offer a simple way of comparing those options.
If you're not into doing the calculations yourself you can go to Handloads.com and use their Energy Calculator- simply type in the details and it will calculate the TKO, momentum and energy of the load in question.