Handguns wound by crushing a permanent cavity. The temporary cavity(imagine the air-space left when you slap water hard...it's bigger than your hand but goes away quickly..thus temporary) doesn't really cause damage for projectiles under 2,000 fps or so. Being the permanent crush cavity is the wounding mechanism, you want it to be as big as possible, so expanding bullets are a good thing.
The thing to keep in mind is that you're also dealing with physics, with a projectile that has only a given amount of energy with which to do work. In this case, work includes everything from temporarily moving tissue away, to crushing tissue to form the pemanent cavity, to even deforming the bullet. When bullets expand, they have a larger frontal area with which to transfer energy to whatever media they're passing through. Basically this means that they'll run out of energy sooner....or that they'll slow quicker and penetrate less.
Read this thread....
http://smith-wessonforum.com/smith-...s/305856-self-defense-ammo.html#post137104467
...for an explanation on why 12" of penetration is understood to be needed for a defensive load. Knowing this, you get a base to work from...you want a bullet that expands as much as possible while penetrating to AT LEAST 12". If a bullet rests between 12"-16", it's pretty ideal.
If you add more energy to the projectile, it can expand larger while resting between 12-16", but will have more recoil and will wear your gun faster. This is where people reflect on their level of training to manage recoil and choose a load that gets a slight advantage in expansion, or a load that is faster to shoot.
As for whether to alternate bullets in the mag or not...don't do it. Given the criteria(penetrating to between 12-16" and expanding as much as possible), a modern hollowpoint will perform much better than a fmj every single time. It doesn't make sense to load a less effective bullet design in to a magazine for a gun you intend to use for defense.
Police generally fire between 11-17 shots for every 1 hit on target. Chances are you'll be much worse as a new shooter. Out of your entire magazine, you may only have one hit somewhere on the threat. You don't want to roll the dice whether it will be an effective defensive load or not. You want every trigger press to send the most effective defensive choice down the pipe...which is a modern hollowpoint.
Also keep in mind that shot placement is the #1 factor in whether a defensive shooting will be effective or not. This places a priority on training well above ammunition choice. I don't want you to think I'm insulting you, that is not my intent, but I do want to offer you something to consider. I'd highly advise you take as many training courses as you can for defensive shooting. Standing at a static range, slow-firing at paper will not really transfer well in a defensive setting.
In defensive shooting, you're likely to be jacked full of adrenaline. Your fine motor goes bye-bye, your eyes dilate and both bug out of your head(you won't be able to close one eye and likely won't even remember seeing the sights at all), you'll likely be shooting in low-light, be shooting while moving, be shooting from an alternate shooting position than what you're practicing, and will be defensively reacting to a threat coming at you. Along with all of that, you may have to clear a malfunction or address concerns like being in contact distance with the threat, being on the phone, manipulating a handheld/weapon mounted light, or pulling kids to safety. You'll have to utilize cover and concealment while knowing the difference between the two. In short, while you feel prepared now, you're not.
Along with training, check in to semi-realistic competition like idpa, IPSC, or 3-gun matches. The time clock really does induce some similar stresses to the adrenaline reaction and you'll quickly identify areas in which you need to improve, like shooting while moving, clearing malfunctions, or utilizing cover.
summary:
1) importance for defensive ammo choice---reliability>shot placement>penetration>expansion
2) training is much more important than ammo choice
3) don't stagger loads, use the most effective defensive load...which is one that penetrates 12-16" and expands reliably
4) ammo I like:
9mm- 147 gr pdx1, hst's, gold dots, golden saber bonded/ 135 gr critical duty/ 115 gr barnes dpx
40- all the above makes and bullets in a 165 or 180 gr. 40 is a weird cartridge in which some loadings have MORE energy AND momentum in the 165 gr, because 180 gr runs out of case capacity. Other loads the 180 gr is better, pdx1 being one of them.
