The .221 is made for 40's. Doing 3450 in my gun they're very accurate and do a great job on varmints. Through a 14TW barrel. I suppose you could go with a 12 twist but it's really not necessary.
About .extraction problems on a regular 700.....the gun I set up for .17MIV was a .223 with an unchanged bolt. Shorten the extractor spring to where the case doesn't go flying but just falls out, and that little case extracts just fine.
