As P.O. Ackley put it, there are some spectacular kills with the .220 swift on large game....and there are also some spectacular failures with the .220 swift. For what its worth, in his first book he stated he had taken mule deer, large burro's at long ranges, and other game and did autopsies to inspect wound channel etc. They were all clean kills. However, bullet selection is key......a varmint bullet is not ideal. Alot comes into play, including velocity at impact, what is struck, type of bullet, etc.....it can be done, but it is not recommended. A partition bullet or controlled expansion would be more ideal (and what the author of the article had used). Unsure what there is available in .220 swift factory as it is commonly loaded for varmints.
I know a local guy who has taken several deer with a .223 loaded with 50 grain v-maxes...in all cases they were one shot kills.