Dirtcrashr had some issues with a set of slim grips he bought for his Sig P220. I recently bought a set for my P220ST myself and they would not fit. It looks like they may be rubbing on the trigger bar spring and the issue becomes obviously apparent when you dryfire the gun. They also will not sit completely flush at the rear. I never even bothered inserting the magazine but it's entirely possible that would have presented a problem as well.
It's a shame because I LOVED the feel of the grips. They're slightly thinner and have far better checkering than the original Sig grips.
Had I bothered to check before ordering I would have seen this disclaimer
"These grips will not fit properly if you have the old style metal mainspring seat. Will fit P220's with the new style black plastic mainspring seat. "
If you want slim grips your only option is to go aftermarket or change out the mainspring housing for the newer plastic ones that Sig now uses. Hogue makes a nice set of slim grips for the P220, but they're $130 and I am not sure if they will fit P220's with either mainspring seat.