[xm177e2]

If the round bounces off the target, counter-intuitively, it gets momentum from the target and actually transfers more momentum. If you had armor which caused bullets to bounce off, they would actually transfer more momentum than rounds that stuck to the armor.

Yes, but the momentum of a bullet is not all that much. The momentum of the bullet as it hits its target is less (because of air resistance) than the momentum when it left your gun. The recoil of your handgun is worse than the sheer momentum the victim feels. If the bullet bounces off, I suppose the momentum could be increased, but what matters is the

momentum/(surface area * time)

(I think--it's been a while since I did any physics)

[Lonesome in Massachussets]

delta_p = Integral [ F(t) dt ] ! integrate over reasonable time boundaries.

delta_p is the change in momentum,
F(t) is force as a function of time
dt is incremental time.

Works every time, else Isaac Newton'll kick your ass. Larger surface area causes an increase in F(t) and increases momentum transfer. If the bullet and the armor are perfectly elastic, in case of normal incidence, the round will recoil with the same velocity (essentially) that it impacted with, and the momentum imparted to the (armored) target will be twice the momentum of the round on impact. If the round sticks to the target, preservation of momemtum requires that all its momentum (on impact) be transfered to the target.