The Colt "Vest Pocket" Pistol. Based on a 1905 Browning design for FN First prototype appeared in 1907. A striker used instead of a hammer and firing pin. Mechanical features. How the safeties work. Thumb safety - grip safety - magazine safety. Operation of the Colt "Vest Pocket" Pistol. Firing cycle explained. The 635 mm Browning or. 25 ACP cartridge.