God's Hammer is a weapon you obtain from Blackbeard very very early on in the game. Progress through the game normally and within maybe 30 minutes of playing, you'll have the weapon. Anyway, the way I did this was that I was basically only using this weapon as soon as I obtained it. Hold down RT to deal more damage aswell. I also recommend upgrading this weapon at the "Sinterpol Armory", right next to the Ultor Tower HQ on your map.