Re: 14 twist barrel and 68 gr .224 bullets
Thats right TBob.
Greenhill shows 10tw for the 69 Sierra, >2800fps & bullet measuring .898" long. But thats marginal really. With more precise software I get a 10tw Sg of ~1.27 @3500fps ICAO conditions. At 2500'ASL, and 75deg, Sg goes up to 1.43.
So 1:10 should work. But 1:9 is perfect - Sg @ ICAO = 1.56
If high enough in elevation, and really smoking it, 1:11 technically might work. But forget any twist slower for that bullet.