The .220 Weatherby Rocket (.220 Swift Improved)
By Chuck Hawks
Roy Weatherby developed the .220 Rocket in 1943. It was the first of the Weatherby cartridges and the only one to remain a wildcat, since Weatherby never offered factory loaded ammunition in .220 Weatherby Rocket. It was the later .224 Weatherby (based on a unique, miniature Weatherby belted case) that was offered in Weatherby Mark V rifles.
The .220 Rocket is an "improved" version of the .220 Swift, with less body taper and a sharper shoulder to increase case capacity. Unlike subsequent Weatherby designed cartridges, the .220 Rocket has a shoulder of conventional shape, not the double radius configuration used for all subsequent Weatherby cartridges. Nor is it based on a belted case; the parent .220 Swift case is a semi-rimmed type.
Simply simply shooting a .220 Swift cartridge in a rifle with a .220 Rocket chamber creates .220 Rocket brass. This blows-out (or "fire-forms') the brass to the shape of the chamber. P.O. Ackley also designed a .220 Swift Improved, which is similar in performance and concept to the Weatherby version, although not dimensionally identical.
The .220 Rocket has a .472" rim diameter, .443" base diameter, .430" shoulder diameter and .260" neck diameter. The case length is 2.21" and the cartridge overall length is 2.68". The Rocket uses standard .224" diameter bullets.
About the last thing the Swift needs in more velocity with light bullets, as it tends to be hard on barrels in its standard form and increasing the powder capacity merely makes the erosion problem worse. Like the Swift, the Rocket should be most useful when loaded to around 3700-3800 fps with bullets weighing about 55 grains.
Reloading data published by P.O. Ackley suggests that 39.0 grains of IMR 3031 powder behind a 55 grain bullet should yield a MV of 3767 fps. 42.0 grains if IMR 4064 behind a bullet of the same weight gave Ackley a MV of 3860 fps. Primer, bullet, and case were not specified.
Due to the .220 Rocket's straighter body and sharper shoulder, case life should be extended compared to the original .220 Swift. This would seem to be the .220 Rocket's principle advantage to the reloader.
Copyright 2006, 2012 by Chuck Hawks. All rights reserved.