Corrected entry: When Jules and Vincent are loading in their guns in the beginning of the film, Jules drops the hammer on his pistol. He does it almost effortlessly, despite the gun supposedly being loaded. The gun he uses is a Star Model B (a 9mm copy of the M1911), which has a hammer, and one SHOULD NEVER drop the hammer on a live round with a 1911 or any hammer fired pistol. Even if done, extreme caution should be exercised, but still shouldn't. He is doing the same when he lets "Ringo" go at the diner.
Matdan97
5th Apr 2020
Correction: Jules being careless with the gun isn't a mistake, it is intentional. Later in the movie Vincent accidentally fires the gun and blows some dude's head off, showing he is careless with it: they are not professional gun handlers; they don't care about any rules.
lionhead