rifled barrel has 6 right-hand grooves and a Swiss Army specification 254 mm (1:10 in) rifling twist rate. Originally the cartridge had a cupronickel-plated steel-jacketed bullet and Berdan primer, but it now has a tombac-jacketed bullet and lead-free Boxer primer. Since 1997 most components of the round are made in Switzerland. United Kingdom Round, 5.56mm Ball, M193: M193 equivalent produced by Radway Green (though some quantities of Hirtenberger Patronen-produced rounds were imported) Round, 5.56mm Ball, L2A1/A2: FN SS109 equivalent produced by Radway Green. Round, 5.56mm Tracer, L1A1/A2 [Red tip]: Tracer round complement to L2A1/A2, produced by Radway Green. Cartridge, 5.56mm Blank, L1A1/A2 [crimped tip]: Blank training round complement to L2A1/A2, produced by Radway Green. Round, 5.56mm Ball, L3A1: M193 equivalent produced by Hirtenberger Patronen for use in AR-15 weapons and the L101A1/A2 rifle. Round, 5.56mm Ball, L15A1/A2: FN SS109 equivalent produced by Radway Green, optimised for use in AR-15 weapons such as the L119A1/A2 rifle. Round, 5.56mm Ball, L17A1/A2: FN SS109 equivalent produced by Radway Green, optimised for use with SA80 weapons. Round, 5.56mm Tracer, L16A1 [Red tip]: Tracer round complement to L15A1/A2 and L17A1/A2, produced by Radway Green. Cartridge, 5.56mm Blank, L18A1 [crimped tip]: Blank training round complement to L17A1/A2, produced by Radway Green. Round, 5.56mm Ball, L31A1: New "Enhanced Performance" design produced by Radway Green since 2016, based on the FN SS109 round but featuring an all-steel bullet for improved penetration and giving similar performance in both AR-15 and SA80 weapons. Round, Drill, L1A1 [chromed body]: 5.56×45mm inert training round, produced by Radway Green. United States Military ammunition was packed exclusively in 20-round cartons from 1963 to 1966. In late 1966 the 10-round stripper clip and magazine-charging adapter were introduced and ammunition began being packed in clips in bandoleers. US Army Cartridge, Caliber 5.56 mm, Ball, M193: 5.56×45mm 55-grain [3.56 g] ball cartridge. This was type-standardized and designated by the US Army in September, 1963. Cartridge, Caliber 5.56 mm, Grenade, M195 [Crimped tip with Red lacquer seal]: 5.56×45mm high-pressure grenade-launching blank. Cartridge, Caliber 5.56 mm, Tracer, M196 [Red or Orange tip]: 5.56×45mm 54-grain [3.43 g] tracer cartridge. Cartridge, Caliber 5.56 mm, High Pressure Test (HPT), M197 [stannic-stained or nickel-plated case]: High-pressure Testing cartridge used when proofing weapons during manufacture, test, or repair. Cartridge, Caliber 5.56 mm, Dummy, M199 [No primer, Fluted case]: 5.56×45mm inert cartridge with fluted indentations in the case. Used for loading and unloading drills during