There have been some interesting innovations in ammunition for personal weapons in the last decade. Prior to this time-period, the last major
innovation I can recall in an ammunition/firearm combo, was in the early 1960s, when MB Associates developed and marketed the GyroJet family of firearms. As I
recall (and understand that my powers of recall
ain't what they used to be), the ammmunition was a "caseless round" (in that it had no separate "bullet") - it was a solid-fuel propelled projectile. Stabilizing spin was imparted via 3 canted ports on the rear of the projectile. The weapon that fired it used a forward-mounted underhammer striking system that drove the round rearward onto a fixed firing pin, and the departing projectile reset the underhammer for the next round. It was touted at the time to shoot a perfectly flat trajectory for 500 yards, but after 500 yards it had a very quick,
very steep downward trajectory (
it dropped like a rock). I also seem to recall that it had some serious problems with misfires, and when it did fire it lacked practical accuracy. As a consequence, it disappeared after only a brief marketing period... but it
was an "innovative concept" at the time. Much like Sandia's winged wonder.
Pax...