Couple things.

Strength plays no part whatsoever in how hard a person can hit. The only role strength has is to generate the speed that actually does matter when you're hitting something. The stuff that matters is mass and acceleration. Since Mifune is airborne, all of his mass is going to be used to power the blow, and he has over 1,000 times the mass of a bullet and half the speed. Herriman is getting knocked on his ass (so to speak) no matter what happens to Mifune's hand.

The next question then, is what DOES happen to Mifune's hand? Since I'm not a physicist, this part is much less clear than the result of getting hit at 500 mph by a 180-200 pound projectile. In all likelihood, the hand would make it through the armor field relatively unscathed, but it would be robbed of a significant amount of its momentum. So the question that remains is which breaks first? The chitin or the claws and hand? Well the chitin is more durable thanks to being a solid thicker piece, but the hand has velocity on its side. Honestly, it could go either way. Since this is a statless RP (and I'm not well-versed enough to pull out the necessary calculations even if it were stat-based), it's pretty much impossible to say for sure which would come out in better shape. My best guess is that both the chitin and the hand would get mangled.