Expansion vs Penetration
Accurately placed expansion bullets plus good penetration without over penetration would be ideal. I'm sure that's obvious but a difficult balance. In practical use, this is what usually happens;
(I'll define "vital" as a large artery, heart, spine or brain.)
1. The bullet expands and comes in contact with a vital.
2. The bullet expands and doesn't penetrate deep enough to come in contact with a vital.
3. The bullet doesn't expand and misses a vital due to the bullets smaller diameter.
4. The bullet doesn't expand and hits a vital due to accurate shot placement.
5. The bullet over penetrates and potentially causes collateral damage.
To consistently achieve the above five possible outcomes, we would need the following:
1. For the first case; A mid to high powered cartridge (1000fps+), with excellent expansion design.
2. For the second case; A low to mid powered cartridge (1000fps-), with excellent expansion design.
3. For the third case; A mid powered cartridge (1000fps).
4. For the fourth case; The same as the third case.
5. For the fifth case; A mid to high powered cartridge (1000fps+).
A mid powered hollow point could teeter between no expansion and under-penetration.
A mid powered full metal jacket could teeter between missed vitals and over-penetration.
It seems that a non-expanding bullet in a high powered cartridge would be the most reliable. Relying only on the shooters ability.
1. FPS alone does not tell you how much damage will be caused but it can tell you if the bullet will expand.
2. A 124 grain FMJ 9mm fired from a barrel which delivers 1,000+ fps should provide adequate penetration to hit a vital with the chance of over penetration.