.220 Swift

Rifle cartridge
the rifle cartridge

The .220 Swift (5.56×56mmSR) is a semi rimmed rifle cartridge developed by Winchester and introduced in 1935 for small game and varmint hunting. It was the first factory loaded rifle cartridge with a muzzle velocity of over .

The velocity of the cartridge ranges from up to about The Swift is a large cased .224 caliber cartridge and bullet that was created for small game such as prairie dogs, groundhogs, marmots and other vermin (or "varmints" in the US). When introduced it was faster than its nearest varmint hunting competitor, which was the .22 Hornet (also .224 caliber). It was found to be an extremely accurate cartridge as well. The .220 Swift is the fastest commercial cartridge in the world, with a published velocity of using a bullet of and of 3031 powder. Due to its very high velocity its bullet drop allows precise sighting to ranges out to , and it is still considered an excellent cartridge for taking varmints by experienced Swift shooters. The original factory load from Winchester provided a bullet launched at Handloaders could marginally improve on this but only at maximum loads. The Swift can be loaded with light bullets to reach In recent times .224" bullets have been developed for use in high velocity .22 caliber rifles for taking larger game and long distance shooting. Heavier bullets perform best in rifles that have an appropriate rifling twist rate taking into consideration the diameter, length, and other physical properties of the projectile.

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 6mm Lee Navy cartridge necked down, but besides inheriting headspacing on its rim from the parent, a feature already considered obsolete by 1930s, the protruding rim which complicates loading was even made larger to fit with 12mm wide .30 06 bolt faces. The .220 Swift was developed by Winchester and introduced in 1935 as a new caliber for their Model 54 bolt action rifle. When the Winchester Model 70 bolt action was first issued in 1936, the .220 Swift was one of the standard calibers offered and continued to be until 1964 when it was discontinued.

The Swift has the dubious privilege of being possibly the most controversial of all the many .224 in caliber cartridges, and has inspired equal heights of praise and criticism. Traditionalists have roundly condemned it as an overbore "barrel burner" which can wear out a chromoly barrel in as few as 200–300 rounds, especially if long strings of shots are fired from an increasingly hot barrel. Its supporters have maintained that the fault lies with poor quality barrel steels and the failure of users to remove copper fouling after firing, and point to instances of rifles with fine quality stainless steel barrels chambered for the Swift, which have maintained sub MOA precision after well in excess of 4,000 shots. More popular, however, is the smaller and slightly lower velocity .22–250.

Due to the cartridge being over capacity for the bore diameter and the extreme velocity of the projectiles, throat erosion is a common problem. Modern metallurgy and cryogenic treatment have vastly improved barrel life with the .220 Swift and other cartridges, although weapons firing these cartridges still usually require rechambering or rebarreling much sooner than those firing lower velocity cartridges such as the .222 Remington and the .223 Remington.

The Swift remains a controversial deer caliber. Its use is prohibited in many US states and also in the Netherlands, England, Wales and Northern Ireland for large deer such as red, sika and fallow, but some states, such as Minnesota, currently allow smaller caliber rounds like the .220 Swift to be used. In the cartridge's early days during the 1930s, expert red deer stalkers such as W. D. M. Bell used the .220 Swift on large stags with great success, and extolled the caliber's seemingly magical killing powers, which they attributed to massive hydrostatic shock waves set up in the animal's body by the impact of the very high velocity bullet. Critics of the Swift have maintained that the light, , bullet leaves an inadequate margin for error in bullet placement for the average deer shooter's skills, and thus invites wounding, which would have otherwise been avoidable. There is, however, little debate about the Swift's proven effectiveness on small deer species, such as roe, provided very fast fragmenting "varmint" type bullets are not used. Most factory Swift rifles come with a fairly slow twist rate such as 1–12 or 1–14 inch, designed to stabilize the lighter bullets popular in varmint hunting. Custom Swifts can have faster twist rates such as 1–9 inch allowing them to stabilize heavy bullets, including those with a construction suitable for larger game. P. O. Ackley maintained that the .220 Swift was a fine round for medium large game and used it extensively for example when culling wild burros in the American West. Famous Alaskan wildlife control officer Frank Glaser also utilized the caliber extensively during the 1930's and 40's. Glaser used the Swift on all sorts of Alaskan big game, including wolves, moose, caribou and Dall sheep, and found that with carefully placed lung shots it would produce more instantaneous kills than any other caliber. However he considered it completely inadequate against grizzly bears, once having to shoot an aggressive sow eleven times to put the animal down.