The armor Nickolaus had ripped from the beasts undercarriage was not random, it was the plates guarding the beasts heart... Nickolaus had no intention of dodging the cats attack.

Nick brought the knuckle dagger in an uppercut, meeting the beast's claw with his armored knuckles. When they met, the knuckle dagger shattered, the iron hard claws raked up his right his right arm, cutting deep, bloody furrows all the way up to his shoulder. However, this is what Nickolaus wanted as it was the perfect opening. In his left hand, his pistol was cocked. Nick slammed the muzzle of the pistol into the beasts exposed skin, and pulled the trigger. Even with its thick hide and muscle, the bullet at that range would pass all the way through to its heart (assuming Nickolaus had remembered a lions anatomy the correctly). With that, he dropped the pistol and threw himself away from the beast, in case it fell over or he had missed it's heart. If he had missed though, there would be little he could do to avoid another charge.