Four inert 20mm M103 rounds in good to very good condition overall. The M103 is a standardized U.S. military specification (20 × 102mm) brass or aluminum cartridge case. It is primarily designed to hold ammunition for the M61 Vulcan rotary cannon, as well as the M39 and M197 automatic guns, and is often sold and collected as inert or fired display rounds. The 20 × 102mm M103 cartridge case is used across multiple branches of the U.S. military. When loaded, these rounds can fire a variety of projectiles, such as the Mark 244 Enhanced Lethality Armor-Piercing (APD) or the M53/M55 series. The high-speed automatic weapons using this ammunition are equipped in various aircraft and air defense systems (including the F-15 Eagle, F-16 Fighting Falcon, and AH-1 Cobra). The M61 Vulcan cannon, which utilizes this brass, fires at a staggering rate of up to 6,000 rounds per minute. Because collectors frequently find fired cases or deactivated rounds at estate sales and from surplus suppliers, they are a common piece of military memorabilia.