Selecting the "best caliber" self defense pistol:
As a firearms dealer I am often asked, "What caliber is the best for self-defense?" The answer to this question is simple. "Whatever caliber you shoot most accurately with is the best caliber for self-defense!"
Much is made of the term 'stopping power' when it comes to caliber. What is really meant by this term is the amount of kinetic energy a bullet can transfer to a target. Kinetic energy is weight of an object multiplied by its velocity/squared. It is measure in 'foot pounds'.
It seems obvious to the casual observer that the most delivered kinetic energy would have the most effect on stopping a threat. All other things being equal (shot placement for example) this would be a true statement. Obviously a 230 gran bullet travelling at 900 feet per second (squared) deliver considerable more kinetic energy at the target than say a 90 grain projectile travelling the same speed.
Having said that, I think we can also agree that being hit in the shoulder by a passing semi-truck (while it would sure ruin your day) is not nearly as devastating as the same truck at the same weight and speed striking you in the chest. Sorry to put it so graphically, but it does illustrate the point.
Recently the F.B.I. and other federal agencies reverted back to the 9mm caliber after utilizing .40 caliber for many years. What caused this decision was NOT that 9mm delivered more kinetic energy, but rather that agents had an easier time placing shots in critical areas more accurately with the 9mm.
Most of us know that the U.S. Army (and other branches) stopped issuing .45 caliber pistols many years ago as a standard sidearm and also made the transition to 9mm.
None of this means that the 9mm has the best 'stopping power' of any caliber in terms of kinetic energy delivered. It does not ! What it simply means is that for many shooters it is easier to deliver shot placement to vital areas with a lighter caliber.
The sad reality is if these large groups would train more to develop proficiency with larger calibers and be able to deliver those shot accurately, the .40 or .45 would be considerably more 'effective'.
The decision to become proficient is a very individual choice. Are you willing to invest the time and money to train and become truly proficient ? While it is very easy on the budget and does teach basic skills, the 40 grain projectile travelling at 800 feet er second of a .22LR will certainly make you a 'bullseye' shooter, but with little more effect than a bee sting on the target, it's not the best choice for stopping a threat. You would be relying on incredible luck that this projectile struck something major. Even then, you would be relying on the target bleeding to death which will take approximately 3 minutes. While it might make a bad guy think twice about continuing his assault, it might just piss him off and make him more determined.
in summation, the choice of caliber is very individual. I cannot tell you what is "best", but hopefully understanding a little more about the choices helps you decide.
If you want to play with the numbers, here is a kinetic energy calculator that will do the math for you.
As always, if you have questions, feel free to ask !