.450 Ackley Magnum
Date: Jun 01 2012
A long the spectrum of today’s rifle calibers, there is little to argue that the .45 caliber is the most predominate and popular of the big bores. This ascendancy started back in the 1870s with the American .45-70 Government and the English .450 Black Powder Expresses. Even in the beginning, we see attempts at improving the performance of the .45s, primarily by increasing case lengths. By 1898 smokeless powders, improved steel and stronger rifles allowed Rigby to introduce his .450 3¼-inch Nitro Express and set the modern standard for relatively light yet powerful dangerous game rifles. From then until after World War II, little interest was shown in furthering the .45s, but beginning in the 1950s and carrying on to today, practically any case large enough to hold a .45-caliber bullet has been necked up, blown out, shortened or lengthened and stuffed into actions of all sizes. While he is best known for his high velocity, smallbore wildcats, the .45s did not escape the attention of the prolific P.O. Ackley, and his .450 Magnum represents one of the largest rounds that will fit in relatively common rifle actions.
Ackley was aware of other similar H&H-based wildcats at the time, such as the bottlenecked .450 Barnes Supreme, the various straight taper Watts cartridges and the .450 Mashburn formed simply by using Norma cylindrical brass. He was also fully aware of the big-bore experiments of Kalispell, Montana, gunsmith John Buhmiller, and one could make a strong argument that Buhmiller’s findings had a significant influence on Ackley’s final design. Buhmiller is given a complete chapter in Vol. 1 of Ackley’s Handbook for Shooters and Reloaders where he describes his experiences in Kenya, testing various big bores on crop-raiding elephants and buffalo. Buhmiller writes that he started with a standard .458 Winchester Magnum due to delays in receiving his “.45 Weatherby” (a .378-based predecessor to the .460) and his “.450 Magnum” (identical to the Mashburn listed above) and credits the .458 Winchester Magnum with fine performance. But, he felt that his .45 Weatherby and .450 Magnum delivered slightly better performance on the large and dangerous animals he was shooting. In the end, he preferred the .450 because it was an easier build than the .45 Weatherby and held more rounds. I’m certain that Ackley knew this and felt that he could squeak a little more performance from the cylindrical H&H case if it were given more capacity by including a slight shoulder and would still maintain the ease of rifle build and magazine capacity. The overall size of the .458 Winchester Magnum may mirror similar thinking by Winchester engineers at that time.
Even without Buhmiller’s input, Ackley’s .450 follows the same formula as the rest of his “improved” cartridges and is formed by taking a standard case and blowing it out to a minimum taper and giving it a sharp shoulder. For the .450, he used the full-length H&H case, kept the 2.850-inch trim length and designed it with a straight neck. It’s unlikely to have been a concern at the time, but some modern students of case design eschew a case design that tapers from base to mouth such as found with the .45-70 and .458 Winchester Magnum, claiming that consistent neck tension and bullet alignment can only be achieved with a parallel case neck. This is a rather fine point to be debating, especially considering that the .458 Winchester Magnum case only tapers 0.007 inch per .5 inch. Other than designing the chamber with considerable freebore, there is little more that Ackley could have done to increase the performance of a .45 caliber on H&H brass.
The standard claim for the .450 Ackley is a 465- to 500-grain bullet at 2,400 fps muzzle velocity. This is reasonable but Ackley’s claim of 2,470 fps with a 500-grain bullet over 90 grains of IMR-3031 is not recommended! One must wonder how he managed to physically get 90 grains of 3031 in this case, let alone the 98 grains of IMR-4320 he lists under a 500-grain bullet in the slightly smaller .450 Watts. The modern reloader is best served by using loads published in A-Square’s Any Shot You Want or starting with modern loads listed for the slightly smaller capacity .458 Lott and carefully working upward. Lighter bullets, such as the fine duo of Barnes 450 grainers, can easily be driven to the 2,400 fps level, but this speed with 500 grainers should be approached with caution. At these speeds, recoil starts to become quite noticeable in the trimmer rifles that H&H-based rounds can be chambered in.
I had the opportunity to play with a .450 Ackley soon after moving to Kodiak in 2004. At the time, the production delays with a Montana Rifle Company Professional Hunter action led me to change to a standard long action. MRC lists the .450 Ackley as an available chambering, so I had them install one of its fine barrels, 22 inches long and with a one-in-10-inch twist on the long action. At that time, I also ordered a Boyd’s JRS laminate stock pre-fit for a long-action Winchester Model 70. Due to the similarities between the MRC and Winchester, bedding the stock required minimal fitting. In addition to epoxy bedding, cross bolts were installed behind the recoil lug and magazine box, and no barrel- mounted recoil lug was needed. I also bedded enough lead in the forend to bring the rifle weight to 10 pounds, and although rather heavy, this stock performed well and was used for bench testing. A standard Bell & Carlson Carbelite was purchased for hunting, and it too was easily fitted but began to crack at the front action screw after a couple hundred full-powered loads. Bell & Carlson is not to fault for this, as it offers a beefed up version of this stock for heavy kickers. Despite the light weight of 8½ pounds with the Carbelite stock, the design delivered recoil well, and only the knuckle on my right hand felt any bite from the kick.