The following is the write-up from Cartridges of the World at reloadbench.com I have been well served by looking up the entries there because they recommend powders that have proven themselves to be excellent in the particular cartidge. There may be better powders now, but at least you have a place to start with this:
Since its introduction in the Winchester Model 54 in 1935, the .220 Swift has been a favorite punching bag of those who seek to find fault with everything in life. First the Swift was put down by wildcatters who were envious of its performance and even today it is a favorite target of those who find it impossible to praise one cartridge without condemming another. Despite its unfair treatment, those who actually have experience with Winchesters big .220 consider it to be the finest factory loaded cartridge available for shooting varmints at extremely long ranges.
Inherently, the .220 Swift is extremely accurate. Recent testing of the cartridge loaded with custom benchrest quality bullets in a Remington 40X rifle produced 25-shot aggregates of less than .270". Another 40X rifle in the same caliber with slightly over 3000 full power loads fired in its barrel averaged .344" for 5-shot groups with various powders. The key to enjoying long accuracy life with the .220 Swift, or any other high velocity cartridge, is to choose a top quality barrel of modern steel, never subject it to a high rate of sustained fire, and the maintenance of its bore by proper cleaning.
As this is written, the Remington 40X, Ruger Models 77 and No. 1, and Ultra Light Arms Model 20 rifles are available in .220 Swift. The Swift is seen at its best when loaded with a good 55 grain spitzer at 3800 to 3900 fps. If you want less velocity, buy a .22-250 or .223. It could be that more IMR-4064 has been burned in the .220 Swift than any other powder and it is a dandy, but H380 and H4895 often produce equally fine performances.
