It sucks when you think you've hit on something revolutionary and then find out that it's already been done. That's what happened today when I shot an e-mail to a friend of mine that reloads. I said I wanted to try a bullet that had a super flat trajectory and could defeat most soft body armor.
My idea? A necked down 9mm to a 22 cal. Maybe even a 45 necked to 22.
The problem.
Armscor has been there and done that! Why it isn't widespread is beyond me but the stats on this little wildcat are impressive. Read a bit about it here.
UPDATE:
Thanks for all the info guys. The more I read about this round the more excited I'm getting about it. It blows the 5.7 away in performance and its potential would make a weapon equipped with it a one shot stopper. The velocity almost rivals that of a rifle. The testing I've seen shows that it penetrates hard targets with ease (I'm talking steel plates). This is definitely going on the wish list.