Ackley Improved
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Ackley Improved (designated AI) rifle cartridges are commercially available cartridges that are "improved" by firing in the AI chamber. The AI version has less case body taper and a sharper (usually 40 degree) shoulder, giving the cartdrige case more powder capacity, thus improving it's performance.
The Term "Ackley Improved" means that the cartridge was documented as being originally altered to the improved version by Parker Oliver Ackley.