Continuity mistake: When Nick and Casey go into Ballpean's flat, nick is frisked by the bodyguard, who finds no weapon on him. Casey refuses to be searched. When a fight breaks out, Casey pulls out two pistols, so we understand how he smuggled them in, by refusing to be frisked. However, Nick pulls a machine gun out from under his jacket. There was no way he could have smuggled this in without the bodyguard catching him when he frisked him. It's a big gun too, which would have made it even more obvious if he tried to smuggle it in.
Continuity mistake: At one point in the film, Casey's penis is out of his trousers and his trousers unzipped as Dallas rapes him when he is tied to a chair. Billy Hill then shoots Dallas and kills her. He then pulls Casey's polo shirt down over his exposed penis - but he does not put Casey's penis back in his trousers or zip up his trousers. When Casey finally unties himself from the chair and stands up, his trousers have magically been zipped up.