There are a few important things to think about when it comes to selecting ammunition for personal protection. One of the most important aspects is the environment in which you are in. Bullets have the ability, in many cases, to go through multiple objects before they stop. We need to remember, from a legal standpoint, that we are accountable for every round that we fire until that bullet stops. Ultimately what we want to do is change the type of ammunition we are using to maximize its effectiveness, but also to minimize any potential collateral damage.
You are going to want to make sure to check your state laws before you purchase or use any type of ammunition, because some states have restrictions on the types of ammunition you can use for personal protection. The three types of ammunition you are going to want to use for personal protection are full metal jacket (FMJ), jacketed hollow point (JHP), and frangible ammo.
Full metal jacket (FMJ) ammunition is essentially a swaged lead core with a copper jacket, designed specifically to get increased penetration on a target. When selecting FMJ ammunition for defense, you would want a lighter bullet weight with a higher velocity. When it comes to personal protection, FMJ excels in rural defensive situations. For example, in some parts of the country we do have predatory animals like cougar and bear. During the winter months these animals develop thicker pelts and have more fat on their bodies to compete with weather. FMJ is going to penetrate significantly more than hollow point or frangible ammunition, making it more effective in rural defense. FMJ would probably not be a good choice for personal protection in the home due to over penetration in urban areas.
Jacketed hollow point (JHP) ammunition will also have a swaged lead core and a copper jacket in addition to a hollow cavity at the end of the bullet with lacerations to assist with expansion. The concept behind hollow point ammunition is to increase the surface contact area of a heavier bullet to transfer more energy on target. JHP ammunition would typically be best suited in urban situations, i.e. within city limits, because it still retains its ability to penetrate, however it will penetrate less and transfer more energy than FMJ. In most cases law enforcement officers use JHP ammo in their primary duty handguns. It may not be a bad idea to check with your local law enforcement agencies to see what they are carrying before making a selection.
Frangible ammunition is more of a special purpose bullet. There are two types of frangible rounds, one specifically designed for competition use on steel reactive targets to minimize spalling at close distances. This type of bullet is going to emulate more of a FMJ design, and should probably not be used for personal protection. The other type of frangible ammo is specifically designed for personal protection, and will have a thin copper jacket and very fine lead shot inside covered by a light wax or plastic tip. The bullet density is significantly reduced and the velocity is rapidly increased. What this bullet is designed to do is to transfer the bulk of its energy on its target while minimizing over penetration. This type of ammunition would be best suited for use inside buildings or residential areas because the bullet will lose most of its energy upon contact with hard surfaces. This type of bullet is extremely effective against organic surfaces and will minimize collateral damage.
Your environment should dictate the type of ammunition you are using. When your environment changes you should subsequently change your ammo to maximize effectiveness and minimize collateral damage. It is also a good idea to test fire the ammunition you intend on using to make sure it functions properly through your firearm. It is advisable not to carry hand reloaded or re-manufactured ammunition for personal protection because it has a higher failure rate than factory new ammo.