The .375 Ackley Improved

By Chuck Hawks


P.O. Ackley became the most famous wildcatter of his generation and many of his creations were "Improved" cartridges. In this case, Ackley Improved the .375 Whelen, a wildcat designed by the late, great gun writer L.R. Wallach and based on a .35 Whelen case necked-up to accept .375 caliber bullets. The .35 Whelen is a standardized cartridge based on the .30-06 case necked-up to take .358 inch bullets without any other changes.

A cartridge is usually Improved by blowing out the case to reduce body taper and sharpening the shoulder. This increases the likelihood of extraction problems (easy extraction is why cases were tapered in the first place), but slightly increases powder capacity, allowing a bit more velocity at the same pressure.

In the case of the .30-06/.35 Whelen case, which has a moderate 17-degree, 30-minute shoulder and medium body taper, Improving has a positive benefit when the case is necked-up to take fat bullets. The .30-06, being a standard rimless case, headspaces on its shoulder. When bullets of .375 or larger diameter are loaded in a standard .30-06 case (necked-up), there isn't enough shoulder left to ensure positive headspacing and the blow of the firing pin may drive the case forward. The Improved case, with its very sharp shoulder of slightly larger diameter, helps prevent this. The original .375 Whelen encountered this headspacing problem and never became popular, so the .375 Ackley Improved is the way to go if you want a .375 caliber cartridge based on the .30-06/.35 Whelen case.

Here are the basic dimensions for the .375 Ackley Improved: Bullet diameter .375 inch, Neck diameter .403 inch, Shoulder diameter .455 inch, Head diameter .470 inch, Rim diameter .473 inch, Rim thickness .045 inch, Case length 2.50 inches, Cartridge overall length (COL) 3.42 inches. Use a standard Large Rifle primer.

There are plenty of good .375 bullets on the market. Common examples range in weight from 200 grains to 300 grains. The lightest of these, generally in the 200-220 grain range, are flat nose, soft point bullets designed for use in the .375 Winchester, while spitzer and round nose bullets in the 225-300 grain range are intended for use in the various .375 Magnums.

Given its case capacity and intended purpose (hunting Class 3 game), the .375 Ackley Improved is probably at its best with bullets in the 235-285 grain range. 235 grain and 270 grain bullets are commonly factory loaded in the .375 H&H Magnum and thus are available from several manufacturers.

Most wildcatters load their creations for maximum performance, regularly exceeding the SAAMI or CIP maximum average pressure (MAP) specified for the parent case and leaving no safety margin. Cartridges of the World, for example, published QuickLOAD data for the .375 Ackley Improved loaded to 60,000 psi, while the SAAMI pressure specification for the .30-06/.35 Whelen parent case is 50,000 psi. These high pressure loads called for a 235 grain bullet at over 2800 fps and a 270 grain bullet at 2690 fps from a 24 inch barrel, which are factory load velocities for the much larger .375 H&H Magnum and excessive for the .375 Ackley Improved. If you want a .375 Magnum, buy one.

More sensible would be to essentially duplicate the performance of the 9.3x62mm Mauser, a cartridge of similar size and purpose (not to mention known capability) for which reloading data is readily available. This would mean loading conventional, jacketed, lead core bullets weighing 225-235 grains up to 2600 fps, 250-270 grain bullets at 2400-2500 fps and 285 grain bullets up to a muzzle velocity (MV) of 2400 fps. These are reasonable maximum velocities and should be attainable at a MAP not exceeding 50,000 psi with suitable powders.

Varget, IMR 4895, H4895, H335 and IMR 3031 powders should all be satisfactory with 235-250 grain bullets. H4350, IMR 4007 SSC, Varget, BL-C(2), H335 and H4895 should be suitable with 270 grain bullets. For the Speer 285 grain Grand Slam bullet, H4350, Varget, H335 and H4895 are possibilities.

With appropriate bullets, the .375 Ackley Improved should be as effective as the 9.3x62mm for all Class 3 game, which is to say excellent. Nothing in North America, including the largest Alaskan or Canadian moose and bears, could stand up to it. The same could be said for African game of similar size.

Obviously, you don't need a .375 for Class 2 animals (deer, sheep, goats and pronghorn antelope). However, with 225-235 grain spitzer bullets the .375 Ackley Improved shoots flat enough to qualify as a potential all-around big game rifle for those wedded to the medium bore calibers.

I suspect that loading 200-220 grain Flat Point bullets, which are intended for the .375 Winchester at a MV of 2200 fps, in the .375 Ackley Improved at 2600-2700 fps MV would create a real bomb that would provide spectacular kills on thin-skinned Class 2 game, such as North American deer. However, serious meat hunters would undoubtedly prefer to use the 225-235 grain bullets intended for these velocities!




Back to Wildcat Cartridges

Copyright 2014 by Chuck Hawks. All rights reserved.


HOME / GUNS & SHOOTING / NAVAL, AVIATION & MILITARY / TRAVEL & FISHING / MOTORCYCLES & RIDING / ASTRONOMY & PHOTOGRAPHY / AUDIO