Here's what I think Gun-knuckles should be like(The Parts, not how It looks like coz It's obvious It's a normal H2H Weapon :P) (>>[Concept]<<)

The Explosion should be a Spread Explosion, like Mini-Bombs. Imagine punching the enemy with a boom! and maybe Time your attack to deal more Damage! >:P Add Materia and you're more Awesome than ever!