Guys, I hate to tell you this but
ALL handgun calibers can be ineffective even with good defensive rounds and proper shot placement.
1) If any of y'all wish to visit Sardis, Georgia with me, we can go talk to a man who resisted arrest by a Sardis PD officer. He was getting the upper hand in the scuffle. Bad move. Officer shot him in the face with a .357 from a distance of about two feet. The bullet entered just to the left of dummy's nose heading for the back of his head. Stopped just short of the carotid artery.
2)19 year old female
walked into the emergency department where I work. She had been shot by some thug in the same place as the man above. 9mm JHP. About two feet. After being shot, she walked over a half mile to the hospital.
In a dozen words or less: caliber makes no difference, shot placement is everything.
Another man came into the emergency department after being shot from very close range. The bullet knocked his front tooth out and was found by the paramedic where he had been standing. .32 ACP. Care to argue that caliber made no difference to him or that, with a different caliber, that would have been completely proper shot placement?
My Dad's first cousin had a girl friend for about ten years and then things got hinky. She told him not to come around any more. He didn't listen. He drove out to her home and she wouldn't let him in. So he proceeded to break through the screen door. Hester proceeded to shoot him in the sternum with a .38 Special. The scar is right on the nipple line. The bullet exited about an inch from the vertebral column. Jim looked down at the hole in his chest and decided that she had been serious about not wanting to see him, after all. He walked to his car and drove fifteen miles to the hospital where he caused no amount of excitement. NOTHING had been hit in his chest with a perfect COM hit with a JHP...I checked with Hester. Jim's doing fine but he stays home with his wife nowadays.
For primary carry, I'd feel adequate with a .38 Special or larger. If I had to use it for defense, I'd remember All of the reasons repeating handguns were developed. 1) There might be more than one of the scoundrels. 2) You might just miss. 3) Sometimes, there ain't but one, you don't miss, and he don't stop.
I've seen more hits with major calibers and good placement that didn't stop the man shot. I've seen a guy who shot himself in the mouth just before coming out of his house to be arrested by the cops. After three days in jail, he pipes up with,"Oh, by the way, I shot myself in the mouth just before coming out to meet you guys the other day." Jailer looks in his mouth. Big clot in the roof of it. Since it's been three days and they feel it must have a defective bullet, they bring him 38 miles to MCG in Augusta by squad car. He walks into Trauma (he is developing a slight limp). We wheel him up to Radiology where he gets off the gurney and onto the CT table. People, he had fragments of bullet throughout his cranium. Not only was he mobile immediately after being shot with at least a .38 Special in the brain but he was still capable of just about anything he ever was three days later. I've had worse limps from twisting my ankle.