Swiftone,
I have put more rounds through a 220 Swift than any other varmint gun I own. a 220Swift is the most unusual chambering I have ever come across there is no secret recipie. for example I can guarantee with a 300WM and 180gr bullets you can find a load that will be awesome with RL22 or H4831, with a Swift you have to tinker with powder to find what it likes, Mine loves 41.5gr Win760 55gr bal tips at 3825fps ( out of my gun this load shoots in the .3's but out of my nephews gun this load shoots in the 3" 's, his gun liked H414). Try several different powders to see what yours likes Win760,H414 ,N160,IMR4064,RL15,and some just love IMR4831. one powder to stay away from is H380 it can shoot one hole groups one day and be a Chernoble waiting to happen the next day. the only other advice I can give you is USE NORMA BRASS ,it will save more headache than you can imagine when it comes time to size your brass (yes I know it is expensive but more than worth the price in a swift)
B