killing lycans in this movie

at the begining when the vamp on horse back is trying to out run several lycans he fires 2 silver projectile throwing sta things from his sword they hit a lycan in the chest and kill it ut thise doesnt seem right

as these lycans are first generation lycans turnd by william and stronger than the lesser llycans from he previous films so how can those 2 projectiles kill it, in underworld 1 raze had three of these things in his chest in human form and he never died or even became weakend, and simple had them taken out.

surely the writers know there already established rules