The .243 Ackley Improved
By Chuck Hawks
Like other "improved" cartridges, the .243 Ackley Improved case is nothing more that the common .243 Winchester cartridge fire-formed in a rifle with a .243 Improved chamber. Essentially it is a .243 with a sharper shoulder and less body taper to increase powder capacity. The .243 Improved still uses .243" diameter bullets and, in a pinch, a .243 Improved rifle can shoot regular .243 Winchester factory loaded ammunition.
Wildcatter P.O. Ackley designed his .243 Improved shortly after Winchester introduced their .243 cartridge in 1955. Just as the .243 Winchester became one of the most popular factory loaded hunting cartridges in the world, the .243 Ackley Improved became one of the most popular wildcats.
In performance the .243 Improved can outperform the 6mm Remington and .243 WSSM when loaded to the same peak pressure, but not the .244 (6mm Rem.) Ackley Improved, although it is only a little behind the latter.
The nominal cartridge specifications are as follows: rim diameter .473", base diameter .470", shoulder diameter .457", shoulder angle 40 degrees, neck diameter .275", case length 2.045", overall cartridge length 2.80".
Reliable reloading data for the .243 Improved is hard to come by. It is not listed in any of the reloading manuals that I own, including Ackley's, and I own a bunch of them. I'd start with published 6mm Remington beginning loads and work up from there, chronographing and keeping a sharp watch for signs of excess pressure. Slow burning powders such as IMR 4831, RL22, WMR, and H450 should be good choices. If I could exceed 6mm Rem. velocities with 95-105 grain bullets by about 100 fps (MV around 3200 fps), I'd stop there.
Cartridges of the World lists loads for the .243 Ackley Improved based on Quick Load computer program data for moly-coated bullets at a maximum average pressure of 65,000 psi, which is too high in my opinion. Not to mention that few shooters prefer to use moly-coated bullets. Under those conditions, Quick Load predicts maximum loads with a MV of 3335 for the Speer 105 grain spitzer bullet.
Since all .243 Improved brass must be fire-formed and reloaded, it makes no sense to me to wear it out prematurely. More moderate loads will get the job done and prolong brass life. After all, the standard .243 Winchester and 6mm Remington have proven that they will do pretty much whatever can be done with a 6mm bullet in the field. If you really think you need around 3300 fps (with a 100 grain bullet) from a 6mm cartridge, you'd be better off with a .240 Weatherby Magnum.
Copyright 2006, 2012 by Chuck Hawks. All rights reserved.