 Lt. Hanna is shown "checking chamber" on his handgun in at least one  scene. This is a trademark of the character Nick Stone in a series  of novels by Andy McNab (qv), who was technical weapons training  adviser on _Heat_ (qv). Although not an uncommon thing to do with a  handgun, it is rarely given such visual prominence in films. Also,  the crews tactics in the bank robbery shootout are notably similar  to the "response to enemy fire" tactics featured in the book and  film of McNabs _Bravo Two Zero (1999)_ (qv).