This has probably been debated ad nauseum in other areas of the threads but I am new so here goes.
I used to carry a S&W 686 .357 or a SIG 227 .45 but in order to cut down on the "omigod he's got a gun" looks and sneers from those who disapprove of me carrying my hand cannons. I bought an M&P Shield 9mm. I am currently going through a myriad of CC holsters but that is another thread.
My main question is this. This 9 has a 3 inch barrel and all my other weapons are at least 4" and I usually go with heavier rounds in those weapons . The question being for self defense should I go with the lighter 155gr rounds, (lighter bullet will accelerate faster and penetrate) or the 147gr (heavier round flies slower but carries more inertia into the target.)
I have read all sorts of theories including the 147 takes more pressure to start it down the barrel therefore it will fly faster and the 115 round gets kicked out of the barrel so fast it has no time to accelerate.
Has anyone seen/heard/done any definitive research on which round will perform better in a defense situation? I would hate to find out at the wrong time that I have chosen an ineffective round.