The Calibre Hunter: Ackley Improved

Byron Pace looks over the family of Ackley Improved cartridges and their originator

I would be surprised if most readers of Sporting Rifle hadn’t heard of the Ackley Improved cartridges. Though only a small handful made it into factory production, the impact and influence of PO Ackley has transcended the history of modern cartridge development.

I have never personally owned an Ackley Improved rifle, though have hunted with them on occasion, and long had a desire to add the .280 AI to my rifle line up. Indeed, this is one of the few cartridges that was taken up as a factory offering when Nosler decided to get it SAAMI specified.

PO was born in New York state and began amateur gunsmithing in his youth. This interest ran deep, and in 1936 he sold the family farm to buy out an old gunsmith in Roseburg, Oregon.

From then until 1989 he made his living in the gun industry, leaving behind an incredible legacy. He was instrumental in the creation of the Gunsmithing School in Trinidad, Colorado, and largely regarded as ‘America’s gunsmith’, writing for several magazines and producing five books.

Though many people today will know him predominantly as a wildcatter, Ackley was also a researcher, often testing firearms to destruction in the search for information. He also produced a number of experimental cartridges, not intended to be practical, but rather to test the limits of firearms.

One of these experimental cartridges was the .22 Eargesplitten Loudenboomer. This humorously named cartridge was developed by Ackley for Bob Hutton of Guns & Ammo magazine, and was intended solely to exceed 5,000fps (1,500m/s) muzzle velocity.

Ackley’s loads only managed 4,600fps (1,400m/s or Mach 4.2), firing a 50-grain (3.2g) projectile. Based on a .378 Weatherby Magnum case, the case is impractically over-capacity for the bore diameter, and so the cartridge remains a curiosity.

The advent of new slower-burning smokeless powders may have changed the equation, though I think it likely to remain only a case study.

Another humorous round, the .17 Flintstone Super Eyebunger, based on the .22-250 necked down to .17 calibre, has been used by Australian gunsmith Bill Hambly-Clark Jr to achieve velocities of 4,798fps (1,462m/s) out of a 52in (1,300mm) barrelled gun.

Though commonly written and referred to, what Ackley Improved actually means is rarely explained. It is worth noting that Ackley said he regretted using the term “improved” in conjunction with these designs. The reason he makes this statement is that not all cartridges show gains in velocity from the process. 

The resulting increase in velocity has a lot to do with the beginning case capacity and bore capacity relationship. In other words, the greater the increased capacity, the better the velocity increase. Ackley did not suggest an alternative name for the improved concept.

Rimless improved chambers, when properly headspaced, allow the shooter to fire the factory parent cartridge in the new, improved (oversized) chamber safely. This is because the cartridge is headspaced on the junction of the neck and shoulder.

Traditional Ackley gauges use a go gauge that is 0.004in shorter than the factory or SAAMI go gauge. Because only a small point on the shoulder is in contact with the chamber, it is easy to crush the shoulder as the bolt closes. When fired, the brass stretches to fill the new improved chamber.

This is what is known as fire-forming and one of the great advantages of these ‘improvements’ with the Ackley criteria. It allows the use of standard factory ammo, even without being formed and reloaded. Obviously, it goes without saying that you will only reap the full benefits if you are shooting with formed cases for that chamber.

However, I have known friends with AI chambers run the factory equivalent round through their rifle when out of reloads. It worked very well.

There are a number of well-known AI cartridges, with the .30-06, .257 Roberts and aforementioned .280 Rem parent cases being some of the best examples. A lesser-known cartridge was the .228 Ackley Magnum, developed by PO Ackley in 1938, although the idea came from around 1936 and was one of his first wildcat designs.

He was looking for a better version of a high-velocity .22 cal rifle. His new design was based around the .257 Roberts case necked down to .22 cal with no other changes.

In a write-up in a book Rifles – A Modern Encyclopedia in 1958, he wrote: “The .228 as I originally made it is nothing more than the .22 Niedner. At the time I had never seen the .22 Niedner and simply necked down the .257 case, but I later found out that the .22 Niedner was a 7mm (x57) case necked down to .22, which make the cartridges identical except for bullets. I used a 90-grain and he used a 70-grain.”

I think it would be fair to say that any cartridge aficionado would have to consider their collection incomplete without owning a rifle chambered in an Ackley Improved cartridge.

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