Re: 69gr. bullet for 22-250???
I owned rifle using the 220 Swift Ackley improved in a Shilen SS 1 in 12 twist barrel, and despite achieving 3,650 fps with the 69 grain Sierra HPBT, it would not stabilise.
Judging from my experience, and others that I have heard, you 22/250 would not stabilise that bullet with a 1 in 12 twist barrel.
However, I found that the Sierra 69 grain HPBT gave very good accuracy at velocities of 3,800 to 3930 fps out of a 1 in 10 twist barrel in my .224 Clark.
After about 1600 shots, I had my gunsmith set back the barrel to remove the eroded throat, and now as a 22/250 AI, that same barrel is giving excellent accuracy with the 69 grain Sierra at velocities of 3200 - 3430 fps. Brian.