It's got to be reliable. Feed into the chamber, fire when the primer is hit by the firing pin and eject the empty hard enough to make room for that next round.
Mine needs to be accurate. Accuracy is often a relative thing. Small groups are what I look for. Yeah, I know, everyone says you can't shoot small groups when you're excited, hurt, etc. But if you have a chance, or a need, to shoot a small spot and hit it then those 4 or 5" groups at 12 yds. won't cut it. And I don't want to run closer to the target before pulling the trigger.
Expansion? Hey, ballistic gel is usually pretty perfectly uniform. Meat and bone is not. I've shot enough wild game with rifles to see bullets from the same box, loaded with the same powder/primers to the same specs do something different today than tomorrow, or even different this afternoon than earlier in the day.
Hollow points are small bullets trying to do what a big bullet does coming out of the barrel - be bigger.
I know "they" say 9MM is effective these days. Do you look at the many videos of police shooting people? Do you notice how many times they shoot and how many time they hit and how long it is before it's over? Sometimes those videos are just downright scary.
Yeah, I carry a 9MM sometimes. A .40 most of the time. And extra mags. I'm too old to run fast and I can't hobble very far.
