copied and pasted form 6mmbr.
Why the AI? Some shooters own a half-dozen .223s and they just want to try something different. That natural curiousity can be reason enough to try a .223 Rem Ackley Improved. But there are also three very logical (and quantifiable) reasons to go with this chambering.
Reason Number One is Speed. Depending on the powder, brass, and barrel length, the Ackley version of the .223 Remington will, typically, deliver from 100 to 140 fps more speed with any given bullet. (Light bullets gain more.) That makes a difference, particularly for varminters looking for a flatter trajectory and more explosive effect on target.
Likewise, long-range shooters will benefit from improved ballistics. The AI's greater case capacity will let you run a given bullet faster, or let you step up to a heavier bullet with better BC.
Reason Number Two is Brass Stability. The .223 Rem AI has a 40° shoulder. Once the cases are properly fire-formed, the steeper shoulder resists case growth. You'll find the AI brass is extremely stable and you won't have to trim the cases as often. Many .223 AI shooters also find they can reload the case many times before full-length sizing is required.
Reason Number Three is Availability of Components. Compared to other "hot rod" cases such as the 22 Dasher or 22 PPC, .223 brass is cheap and plentiful. You can buy new IMG (Guatemalan) brass from Wideners for $89 per 1000 cases. Top Brass (Scharch Mfg.) offers fully processed, once-fired Lake City military brass for the same $89/1000. And many shooters already have an ample supply of .223 Rem commercial brass. Rather than let that old .223 brass languish--Ackleyize it.