Introduced by Winchester in 1935, the 220 Swift was the first commercial cartridge to break 4000 feet per second--and it is still one of the few that reaches that speed. Oddly and uniquely, it is based on the long-forgotten semi-rimmed 6mm Lee Navy case necked down. Intended--and extremely effective as--a long-range varmint cartridge, it got a bad rap as a barrel-burner and has never been extremely popular. All cartridges that approach this velocity are hard on barrels...but it's certainly better today than with 1935 barrel steel! Loads vary, but 50-grain loads hover around 4000 fps; lighter bullets are a bit faster and heavier bullets are a bit slower, but the 220 Swift is still the fastest (and thus flattest-shooting) commercial 22 centerfire. Accuracy is generally excellent, and the 220 Swift is chambered in a good selection of factory rifles and loaded by all major ammunition manufacturers.
