Anybody got any idea what kind of velocity increase to expect out of the 22-6AI over SwiftAI, same barrel length? I'm considering a fast twist using 68,69's, or 75 A-Max, for long-range hunting.

The 220 Swift AI (40 degree shoulder) that I used had a case capacity of 55.4 grains, and would drive the 69 grain Sierra HPBT to 3700 fps, and the 74 grain RWS to 3550 fps. The rifle used was a Rem 700, with a Shilen 25.25 inch, 1 in 10 twist barrel.

The .224 Clark (22/257 Roberts Imp 30 degree shoulder)is the ballistic twin of the 22/6mm AI. In my rifle (Rem 700, Shilen 25.5 inch barrel) the case capacity was 63.8 grains, and the Clark would achieve 3900+ fps with the 69 grain Sierra, 3800+ fps with the 75 grain Hornady Amax, and 3700+ with the 80 grain Sierra HPBT.

If you do not want to use a bullet heavier than the 75 grain Hornady Amax, then I would use the 220 Swift AI. However, if you want to use the heavier 80 - 90 grain bullets, then the extra capacity of the 22/6mm AI (or 224 Clark) is then an advantage.
Brian

you will also see more benifit if you go to a 30" or longer barrel- to use all of the slow burning powder the case will hold.

Hi SScoyote,

The velocity you could expect from an ackley improved .220 Swift with a 1:7 30" barrel is as follows:

80gr Berger 3,650fps
90gr JLK 3,330fps

Cheers,
Des.