If it has to be a non-expanding bullet, why not just go to a flat point? The increased terminal effect on tissue by simply changing from a round nose to a flat nose has been seen in countless examples on game and humans since Elmer Keith's days at least.
Physics is physics. If the weight of the bullet or the velocity is increased, recoil increases. And no matter the opinion of smart people like us, .gov is intent of having women and males of questionable masculinity in combat arms and that means no heavy recoiling handguns.
So, it would seem to me the obvious choice to increase lethality without changing the recoil characteristics of the 9mm is a FMJ flat point or WFN. The profile wouldn�t be any different than a HP so feeding should be a non-issue.
That, or a much lighter projectile at much higher velocity ala the 5.7x28 or some new round of our own creation with similar ballistics.
I know that doesn't address the barrier penetration or armor penetration characteristics and my knowledge in that area is sketchy, but if barrier/body armor penetration is a primary goal then increased velocity or a much heavier projectile are the only means to achieve that (AFAIK), and without increasing recoil that means a lighter projectile going faster.
