In previous posts we have covered some of this. But I want to be a bit more specific and make some recommendations.
- Newton's Third Law of Motion. Basically, for ever action there is an equal and opposite reaction. Two people on roller skates pushing off of each other will depart each other in an equal and opposite way (other factors being equal). Think of your bullet (projectile) as skater 1 and your gun as skater two pushing off of each other. Of course mass and a few other factors weigh into the effect, but basically you bullet will impact with similar force to what you felt when firing the projectile.
This factors into my previous posts on the Myth of knock down power. Generally handguns have either NONE or very little. Hollywood has done us no favors here. When targets go down from being shot with a handgun it is because it was a "good" shot landing in a critical area incapacitating the target, or it was because of a mixture of physical and psychological factors associated with being shot. Factors like fear and pain. Even modeling behavior. You are supposed to stop and fall when you are shot... so you do!
- Kinetic Energy. Or as we like to say... damage or knockdown power. Mass times Velocity Squared. The energy imparted on the target is the mass of your projectile times the speed/velocity of your projectile. The heavier the projectile (mass) the more damage. The faster the projectile (velocity) the more damage.
This means that given a choice you GENERALLY will always opt for more speed to gain more damage. Why?? Because Velocity is Squared. It follows that more speed adds an exponential increase in damage. The exception being pistol rounds. A good rule of thumb would be 2000 ft per second.
Until your projectile is traveling MORE than 2000 ft/s you should opt for a larger and heavier bullet to do more damage. Why? Until you are traveling around 2000 ft/s the secondary wound channel will be too small to produce significant damage. There are two wounds a bullet makes. The primary wound channel is roughly the size of the projectile entering the target. The secondary wound channel is based on the speed the bullet is moving through the target. It is like waves coming off of a boat. Or a rock thrown into a pond. The faster you throw it the bigger the ripple or waves.
This "wave" is your second wound channel that in high velocity does so much damage.
So what does this mean in terms of Personal Defense.
- be able to accurately fire your handgun. An accurate shot will do more good than two or three that get no where near a critical area.
- shoot as much gun as is prudent. If you can handle a 45 acp and it is practical to have it with you... have it with you. If it is going to be a "left-it" gun, drop a caliber and use a gun you will tote. (left-it in the house, left-it in the car, left-it on the night stand)
- if possible and prudent always opt for a high velocity rifle. If you live in an apartment surrounded on three sides by neighbors, I am not sure a rifle is best. If you have children, and in a home defense situation you would need to move from your location to their's, a shoulder fired gun might not be best. This depends on you, your situation and aptitude with a rifle.
- no matter what gun you use practice and expect to put multiple rounds on target. In terms of stopping power... more is better. Accuracy is best.