Your most probably have a 14" twist which limits you to shorter/lighter flat base "varmit" bullets..... which will turn the neck or lungs into jello just fine. Tell your friend to avoid quartering meat shots and it should work just fine.
Many of the light weight, flat-base varmint bullets won't even make it to the lungs, if they hit the shoulder; and especially if they hit bone. They are incredibly fragile at .220 Swift velocities.
For my own 1:14" .220 Swift, I gave some 53 gr Barnes TSX FBs a try. They shot well, but I never got a chance to use them on game. I'm sure the petals would shear off if the shoulder was hit, but the base should penetrate and do some nice internal damage.
I would be hesitant to use a Sierra GameKing in the Swift. They're designed to be used at .223 Rem velocities.