Bravo good post!
I think you bring up many good points as well as contraversal thought.
Depending on the firearm, cal, size, and the amount of spare magazines you keep with you, I feel your choices are only limited on those factors. If you carry two extra magazines in addition to the one in your gun and all of those magazines are double stack and you don't live in a state that limits the amount that magazine can hold I cannot see any reason to not load the last mag with a few FMJ's. On the otherside of the fense if you are carrying a five shot revolver with only one reload I would think that having all Hp's would be only to your advantage.
Now lets take this a step further by talking about the gun. Full size five inch barrel with full size grips? Or are we talking subcompact with only three inches of barrel and a tiny grip that usually leaves the pinky swaying in the breeze.
The difference is important because most defense loads are rated and tested using a 5 inch barrel. Reducing this down to a four inch barrel will mean at least a quarter percentagereduction in fps because less powder is going to be used. What does all this mean? Using a 3 in subcompact could potentially leave your Hp's without enough speed to properly expand making them at best justa FMJ upon impact anyway.We have not even gotten into theimportance of proper grip. Limp wristing can have a small effect on velocity as well. Studies are underway to find outjust how much, but a limp grip may mean the difference of 10 to 30 fps. So having a fullsize grip and proper grip technique is important!
Ammunitions company are now stepping up the game. Speer now offers HP's specifically designed for short barrelled auto's and revolvers. This ammo expands at much lower velocities and is more effective when shot out of said firearms. But still you are going to deal with the draw backs of limited ammo supply in the first place when using a subcompact or snub revolver.
I carry a 1911 single stack. If I am going out and about for an extended peroid of time that may involve being out during the evening hours I will carry my Flashlight, knife, OC sprayand 1 spare mag. If I am only staying in town and don't plan to be out past sunset without stopping at home I will only carry my gun, OC sprayand knife. I load both my magazines with Winchester Ranger SXT's 230gr. It is my deepest hope to never have to usethem. And if at all possible in all situations I will always try and retreat if it is safe for me and others.I practice more with my verbal skills and situationalawareness skills thanmost I know. If it came down to a shoot out with both of us behind cover I have no problem letting him expend his ammo while I wait patiently and call the police.