It's possible. Armor has changed and with it the way ballistic weapons work in order to counter armor. In Destiny, ARs use oversized slugs. As such, I suspect that the attempt of the weapon tech is no longer to punch holes in the armor (despite AP rounds existing) and instead to transfer enough kinetic energy through the armor to kill the wearer. With such an approach, it'd make sense if the bullets had lower velocities than current and had poor ballistics performance in holding velocity.