From Internet Movie Firearms Database - Guns in Movies, TV and Video Games
Issues associated with the gun and plot twist
I've always found this movie's plot twist, which revolves around the murder weapon, to be kinda ridiculous. Key problems:
- Crawford's Glock 21 is deemed inadmissible as evidence at the trial when it is revealed that it is so new that it has never been fired (because Lt. Nunally's own Glock was the actual murder weapon). Any modern gun gets test-fired right off the assembly line at the factory, ergo, it's impossible that the gun was never fired. Also, the 2nd Generation Glock 21 had been out of production for almost a decade in 2007, which means that unless Crawford's gun had been someone's safe queen for more than 10 years when he bought it, it's almost impossible that it was so new that it had never been fired.
- How did Crawford swap the guns without anyone noticing, when he had fired four rounds from his own Glock, while Nunally never fired his weapon at the scene? Didn't anyone notice that the Glock recovered at the scene was fully loaded, whereas Nunally's gun (which he never fired) was missing four rounds in the magazine? Did Crawford swap magazines, not just guns? Or did he take four rounds from Nunally's gun at the hotel, and planned to fire exactly four during the murder? (If it's the latter, we're assuming Nunally doesn't notice the reduced weight of four missing rounds on a weapon he's carried on his hip every day for years - also a stretch.)
- The viewer is expected to believe that a DA who (presumably) knows nothing about guns is the first person to notice that Crawford and Nunally had the exact same weapon. Yet none of the police detectives, including Nunally himself, notice how odd it is that Crawford bought a gun that was identical (same make, model, caliber, and generation) to the service pistol carried by the man who was having an affair with Crawford's wife.
- Beachum is unable to get ahold of the bullet in Crawford's wife's skull, and thus unable to match it to the murder weapon, until she dies. A .45 ACP round fired a few feet away into the side of somebody's face is probably not going to get stuck in their skull - it's more likely to go straight through and penetrate walls behind them.