Jason, I'm not sure where the yaw theory came from, but it doesn't work. The bullet is travelling at 2500fps, and spinning at several thousand revolutions per minute. The gyroscopic stability is impressive with those kind of figures.
A badly corroded crown might possibly impart a tiny bit of yaw, but not enough to worry about.
The bullet diameter is .264", leaving 18 thou either side for a 30 cal moderator, assuming that the hole diameter is exactly to .3".
The original question was can I use a .25 cal moderator. The 6.5 bullet diameter is .264", a .25 cal bullet has a diameter of .255". Assuming the mod hole is slightly larger than the .255", you may well be cutting it very fine, if indeed you have a clearance hole at all.