The first commercial cartridge to exceed 4,000 fps. For over two decades it was simply the fastest thing you could buy in a sporting goods store.
Type: Rifle
Introduced: 1935, United States
Parent case: 6mm Lee Navy
Standardization: SAAMI
Bullet diameter: 0.224" (5.69 mm)
Case length: 2.205" (56 mm)
Overall length: 2.68" (68.07 mm)
Max pressure: 62,000 PSI
Rim type: Rimless
Primer: Large Rifle
Typical twist rate: 1:14
Muzzle velocity: 3700–4200 fps
Muzzle energy: 1215–2154 ft-lbs
Effective range: 400 yd
Common bullet weights: 40, 45, 50, 55 gr
Primary use: Varmint
Production status: Active
Also known as: 220 Swift · 5.56x56mmSR
History: Winchester introduced it in 1935 for the Model 54, then the Model 70. Based on the 6mm Lee Navy case necked to .224. Achieved stunning velocity for the era and set benchmarks that weren't surpassed commercially for decades. Gained a reputation as a barrel burner but remained the definitive varmint cartridge through the 1950s.
Notable firearms: Winchester Model 70, Ruger No. 1, Savage Model 12
Similar cartridges: .22-250 Remington, .223 Remington, .204 Ruger