The 7x57mm Ackley Improved
By Chuck Hawks
According to the Cartridges of the World, edited by M.L. McPherson, the 7x57 Ackley Improved remains one of the most popular wildcat cartridges. This is understandable, as the 7x57 Mauser parent cartridge is a world favorite and perhaps the mildest cartridge (in terms of recoil) widely accepted for "all-around" (CXP2 and CXP3 class) big game hunting.
The idea of an improved 7x57 thus has understandable appeal. Of course, to improve such a cartridge's ballistic performance, the price must be paid in increased recoil. Build a 7x57 Ackley Improved on a standard (.30-06) length action, which allows seating bullets long in the case, and maximum (60,000 psi) loads will allow ballistic performance in the .280 range. Because it has greater case capacity the 7x57 Improved, loaded to similar pressure in a strong rifle, will handily outperform the newer 7mm-08 Remington. Of course, as already mentioned, the recoil energy will now approach .280 levels.
The most convenient way to make 7x57 Improved brass is to fire form standard 7x57 brass in an Improved chamber. Norma brass, with its thick case neck, is regarded as the best brass for "improving."
The normal twist for a 7x57 Improved rifle barrel is 1 in 10". The normal case dimensions for the 7x57 Ackley Improved are as follows: rim diameter .473", head diameter .471", shoulder diameter .457", neck diameter .319", case length 2.235". The overall cartridge length is supposed to be 3.06" and bullets are standard .284" diameter.
7mm (.284") bullets are widely available to reloaders in weights ranging from about 100 grains to 175 grains. In a general sense, bullets weighing 120-130 grains are usually intended for hunting CXP2 (deer size) game. The 139-150 grain bullets are usually the general purpose 7mm projectiles, while the 154-175 grain bullets are the usual choice for hunting CXP3 game, such as elk. The 7x57 Improved has a case capacity capable of making good use of all of these bullet weights.
I like a 139-145 grain bullet for most purposes in any standard (non-magnum) 7mm cartridge, and that includes the 7x57 Improved. P.O. Ackley's Pocket Manual lists loads for 140 grain bullets in his 7x57 Improved that included 49 grains of IMR 4064 for a MV of 3008 fps and 35 grains of IMR 3031 for a MV of 3124 fps. Those are maximum loads! Ackley did not specify the brand of bullet, case or primer used in his loads, as he thought those details inconsequential and so stated in his manual. Subsequent testing has proven him wrong. Reduce powder charges 10% and work up carefully, chronographing and checking for signs of excessive pressure.
Among wildcats the 7x57 Ackley Improved has the advantages of readily available brass, the ability to fire factory loaded 7x57 ammunition safely, and a very wide selection of suitable bullets. The performance of this medium size cartridge is excellent, and the hunter with a good 7x57 Improved rifle has little need for any other 7mm caliber.
Copyright 2006, 2013 by Chuck Hawks. All rights reserved.