The 220 Swift was developed by Winchester and introduced in 1935 as a new caliber for their Model 54 bolt action rifle. The prototype for the 220 Swift was developed in 1934-35 by Grosvenor Wotkyns who necked down the 250-3000 Savage as a means of achieving very high velocities. However the final commercial version developed by Winchester is based on the old 6mm Lee Navy cartridge necked down. It is a semi-rimmed case. The 220 Swift was and still is the fastest commercial cartridge in the world. It is also one of the most accurate super velocity 22 cartridges ever developed. Its popularity has benn somewhat retarded by the fact that the ammunition in this caliber is expensive. Factory ammunition has always featured the 48 grain and 50 grain bullets, but the Swift is considered adequate on all animals up to deer size. There is certainly plenty of field evidence to demonstrate on occasion it will give fantastic one shot kills on deer and antelope. However the 220 Swift tends to be erratic in its performance on large animals, and most states will not permit its use on big game of any kind. Properly constructed bullets would almost certainly solve this problem on animals to mule deer size. In any case, factory bullets are designed for quick expansion on light animals. Most varmint hunters agree that the 220 Swift is the best varmint cartridge made. 

This text is based on information from “Cartridges of the World”, Hodgdon reloading manual, the cartridge designer and/or own resources.