Cooper Arms Model 21 in 220 Swift. The 220 Swift is the original high-velocity varmint cartridge, introduced by Winchester in 1935 and still the fastest commercially loaded rifle round. Cooper's tight-chamber, hand-lapped Model 21 brings out the Swift's accuracy potential while managing its reputation for throat erosion through quality barrel work. For the varmint hunter who wants the most velocity available. Type: Rifle Action: Bolt-Action Caliber: 220 Swift Capacity: 1 Year introduced: 1991, USA Weight: 57 oz Overall length: 43.5" Status: Active Intended use: varmint hunting