Then his "I'm smarter" moment was a bit of a stretch. The idea that he could have shoved a shell into the barrel of the machine gun in the middle of a fight with the other guy not noticing and then be so confident that it would kill the bad guy and not hurt him that he just stands there and lets the guy shoot at him is kind of ridiculous.
I didn't even understand what he claimed to do. He pulled a bullet from the belt and shoved it in the barrel. You mean, where bullets go? You put a bullet where bullets go? Maybe he meant the front of the barrel? OK fine, that could cause problems. Most likely the bullet would shoot out and hit you but if you shoved it in hard enough it would bulge the barrel. But to make the bullet shoot backwards? Even bugs bunny didn't fuck up the physics that bad.