I haven't, so far, had the gray smoke trail problem in a .223 - but I have sure seen it in the .22-250 and .220 Swift. One thing you imply in your post, Mike, is that a .223 with a 12" twist might provide similar stability as a .22-250 with a 14" twist? Because of the RPM similarity? While you can make up for twist by increasing the speed - speed doesn't help anywhere near as much as it one would think.

This became very apparent a few years ago when I was playing around with a caliber called the .300 Whisper. It shoots .308 rifle bullets at just below the speed of sound. I was almost shocked to find a 200 grain Sierra Matchking was completly stable and accurate out of 1:10 twist at these speeds. A 1:8 twist was good for the 240 Sierra Matchking. Not much different than much bigger calibers driving these bullets almost three times as fast.