Let's see, what kind of handgun ammo advances have I seen . . .
"Super Vel" is the grandaddy of all current high performance ammo. Maybe it wasn't actually the FIRST of its type, but it certainly popularized the general design philosophy of JHP bullets at higher velocity for personal defense. (But I still think a good HBWC seated backwards makes a helluva self defense load for a .38 Special snubbie.)
I remember "Exploder" ammo . . . carried a primer in the nose with a small explosive charge. Thing is, they weren't very reliable and the chemical energy of the explosive was appreciably less than the kinetic energy of the projectile. (Met a guy at the range making his own - he was taking primers apart and stuffing the priming compound from, oh, I forget, but a WHOLE BUNCH of primers in a JHP he'd drilled out. He still seemed to have all his fingers attached, but I still declined his offer to try some of his bullets out myself.)
About 30+ years ago, I remember a local gunshop outside of Chicago (!) was selling "mer-cor" component bullets; they contained mercury and IIRC the nose was sealed off with a bit of gunk that looked like asphalt. Pretty pricey even back then . . . and I certainly wouldn't want to get hit by one.
Glaser Safety Slugs? Hardly ever hear about them any more, though they're still being made.
KTW ammo - originally made of a tungsten alloy and coated with Teflon - was the subject of dishonest NBC-TV reporting about armor piercing "cop killer" ammo, when it was sold only TO cops. Probably worked a little better than the old conical point Winchester-Western "Metal Piercing" .357 ammo that dates back to at least the 1940s.
But I still consider these to be evolutionary rather than revolutionary steps - the closest thing to an attempt at a revolutionary step I can recall was the Gyrojet Rocket Pistol, which aside from cost, simply didn't work very well.
