Models of the Thompson .45 submachine gun are seen at the 142nd annual National Rifle Association(NRA) Convention at the George R. Brown Convention Center May 4, 2013 in Houston, Texas.The Thompson was also known informally as: the 'Tommy Gun', 'Trench Broom', 'Trench Sweeper', 'Chicago Typewriter', 'Chicago Piano', 'Chicago Style', 'Chicago Organ Grinder', and 'The Chopper'. AFP PHOTO / Karen BLEIER