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African Outfitter Back Issues: CONTENTS – June / July 2007 – (Vol 2/4)

The .450 Ackley Magnum – Roy Vincent

In recent years, we have seen the introduction of many .458 caliber-based factory cartridges like the .450 Dakota and the .450 Rigby.

The .450 Ackley Magnum - LionMy son Alan (right) used his .450 Ackley to stop this lion’s charge

Yet, we tend to forget that Wild Cat cartridges like the .450 Ackley Magnum has a long history of service to hunters of dangerous game. It achieves the ‘mythical’ performance level of 2300–2400 fps with 500 grain bullets considered to be ideal, especially for professional hunters who are often in a situation where they have to back up hunting clients in dangerous situations and where a cartridge that does the job is essential.

Components for the reloader are freely available and relatively inexpensive. The .458 diameter has the widest choice of projectiles available of all the big bores. The case diameter allows a 5 to 6-round magazine capacity in some rifles, and in a pinch, even other ammunition can be used, when the airlines lose suitcases with vital ammunition.

Designed by P.O. Ackley in the early 1950s the .450 Ackley pre-dates the .458 Winchester Magnum and in the opinion of many, should have been produced by Winchester in 1956 instead of the .458 Winchester Magnum, whose limited powder capacity at the time gave rise to some serious problems. However, the development of modern propellants has improved the handloader’s situation giving the .458 Winchester Magnum performance to match and even exceed the original velocity of 2130 fps with 500 grain bullets without excessive powder compression.

The .450 Ackley provides a worthwhile velocity increase over the .458 Winchester Magnum of approximately 200–400 fps, and 100–150 fps over the .458 Lott, depending upon whether factory loads or hand-loads are compared and what propellants are available for hand-loading.


The .450 Ackley Magnum - LionA nice buffalo shot in the Chete Safari area

When Parker Ackley brought out his .450, there was a lot of wildcatting taking place which led to many variations of .450 caliber cartridge designs. Most of these were for use in magazine rifles based on the .375 Holland and Holland, belted magnum, case and in the larger calibers the .375 H&H Magnum case was obviously necked up and expanded in different ways. There is a limit to how many forms can be provided from a single cartridge type. This resulted in many cartridge designs being very similar even though they were developed independently of each other. The performance levels and field results were often indistinguishable from one another. Among the .450 cartridges, the .450 Barnes supreme is with some very minor dimensions identical to the .450 Ackley, but did not become as popular with shooters as did the Ackley version. The .450 Watts, .450 Mashburn Magnum and the .458 Lott are identical to each other with the exception of the Lott’s nominal cartridge length being 2.800″ instead of 2.850″. More discussion about cartridge length follows further on.

The .450 Ackley and Barnes Supreme can be accurately described as improved versions of these three cartridges, i.e. with minimum body taper resulting in a shoulder and parallel neck section giving a more uniform neck tension to the seated bullet. The constant taper on the others results in uneven tension on a seated bullet. The practical effect of this is of no consequence. However, the bulge on the case created by the seated bullet is obvious on closer inspection.

All of the above-mentioned cartridges can be safely fired in a .450 Ackley chambered rifle, the possible exception being the Barnes Supreme as it is so similar that minor variations in dimensions could prevent chambering. However, if it can be chambered, it can be used as long as it is a known ‘safe’ load. Examples of Barnes Supreme must be very rare and unlikely to be encountered. Many owners of .450 Ackley rifles have taken to using .458 Winchester Magnum ammunition when Ackley ammunition was unavailable or too expensive. Now that .458 Lott is factory loaded it can also be used. The fired Lott cases are simply fire-formed to the Ackley chamber. The .458 Winchester Magnum cases fired in the Ackley chamber form a small neck (about 1 mm long). This does not preclude re-loading these cases. Resizing in a .458 die brings the neck back to the correct dimensions. The stretching of the brass will reduce case life to less than it would be if fired in a .458 chamber.

Surprisingly, when the .458 Winchester Magnum rounds are fired in a .450 Ackley chambered rifle there is very little velocity loss. This is contrary to expectations due to the longer bullet travel before engaging the rifling lands, creating, in effect, a long free-bore (throat or leade)

I have personal experience involving about a dozen .450 Ackley rifles firing .458 Winchester Magnum rounds. All of the rifles were converted from .458 Winchester Magnum to .450 Ackley and were fired before and after rechambering to check the velocity loss resulting from the change. In all cases the velocity loss was minimal and usually not more than 20 to 30 fps, which is within the shot-to-shot variation of individual rounds, manufacturing lots and brands.


The .450 Ackley Magnum - LionRoy Vincent with a 65LB Wankie elephant bull

Factory .458 Winchester Magnum rounds of various makes and vintage – some very old – fired in several different rifles chambered for the .450 Ackley, produced velocities ranging from 1923 fps to 2107 fps. The velocity spread is again within the expected variation of .458 Winchester Magnum factory ammunition fired in factory standard .458 Winchester Magnum chambers.

When using other cartridges in the .450 Ackley rifle, particularly the .458 Winchester Magnum, it is essential to re-zero the sights. Experience has shown that there can be a considerable change in point of impact, depending on individual rifles characteristics. This can result in point-of-impact changes exceeding 12 inches (300 mm) at 100 metres. This is not surprising as there can be up to 400 fps velocity difference with 500 grain bullets.

Factory-loaded ammunition is currently made by A-square and Superior in the USA. The cost of this ammunition in South Africa is no doubt very high and availability problematic due to lack of demand. This means that large-bore rifle enthusiasts need to hand-load ammunition to reduce cost and for the enjoyment this gives those of experimental inclination. Fortunately, there are a wide range of bullets available in .458 diameter ranging in weight from 300 grains to 600 grains in both expanding and solid form. Many premium hunting bullets are made for big game hunting by most bullet makers including our own South African makers, such as Stewart Bullets and Rhino Bullets, among others. Ken Stewart at Polokwane makes cases with the correct head-stamp and there is a strong possibility that ammunition will also be available in the near future.


.450 Ackley ammunition can be made from commonly available .375 H & H Magnum cases. There are different methods of achieving this as described below:

Method 1: This the method I prefer. Expand the cases as fully as possible using incremental sizes of expander plugs up to .510″ diameter. Full-length size, with the die carefully adjusted to headspace on the shoulder. R.C.B.S. makes expander die .375″ – .458″, which can be done in one pass. Additional tapered expanders can be turned on a lathe with diameters from .450″– .480″ and .480 – .510. They are then drilled and tapped to fit the expander rod of the die. A normal working load can then be used resulting in the remaining unexpanded section of the lower part of the case fully fire-forming to fit the chamber. Some prefer to anneal the neck and shoulder area before the expanding process to reduce splitting. I have found doing so can result in insufficient neck tension of seated bullets. If the correct heavy duty case lube is used and care is taken expanding incrementally very few cases, if any, will split. Nickel-coated cases seem to be more likely to split than plain brass, so I avoid them if possible.

Method 2: Expand the case neck only as far as is necessary to accept a bullet of choice used for fire-forming, such as cast or less expensive 300 grain bullets. Neck size in the die. This ammunition can be used for practice with powder charge producing sufficient pressures to fully form to the full case dimensions in the chamber.

Method 3: Fire-forming cases without using (expensive) bullets can be achieved by using sufficient pistol/shotgun powder, approximately 20 grains or more as required to fully form the cases to the chamber. Tamp wads of toilet paper down tightly over the powder to fill the case. Alternatively powder charge, followed by a wad of toilet paper, mealie meal, and another wad of toilet paper to keep everything in place. Point the muzzle vertically and fire. The report of these loads is very loud and it makes a mess, and it might even be possible to start a fire. Wear hearing and eye protection, and do not point the rifle at anybody as it can kill at close range. Uneven case mouths sometimes result using this method. Some trimming would then be required to eliminate the unevenness.


The .450 Ackley Magnum - LionFrom left: .450 Ackley; .458 Lott; .458 Winchester Mag; the next two are both .450 Vincent Long; and the last two .450 Vincent Short

When using .375 H & H cases to form .450 Ackley case a shortening of the case to less than the nominal 2.85″ will occur. Trim all cases to 2.76″ or to the length of the shortest case if one wishes to crimp the bullet. I suspect this shortening of the cases is the probable reason the .458 Lott case length is normally stated as 2.80″. The crimping cannelure will not be in the correct position due to the shorter cases, requiring the bullet to be seated too deeply if a crimp is to be in place. Unless a canneluring tool is available it is best to do without crimping. My experience has shown that the neck tension and a full or slightly compressed powder charge keep the bullet secure, unless left in the bottom of the magazine while the rifle is fired repeatedly. Be sure to cycle the bottom round to the top before topping up the magazine. .416 Remington Magnum cases can be used, requiring much less dimensional change to conform to the .450 Ackley chamber. The resulting cases are longer than those made from the .375 H & H.

Cast bullets work very well with the .450 Ackley and can give excellent results on game. It is best to stay with gas check design. Cast bullets of up to 550 grains can be driven to over 2100 fps if desired, depending upon the alloy used in casting.

Locally, the most suitable propellant for this cartridge has been Somchem S341 due to it’s medium burning rate and, importantly, its bulk density allowing heavier charges than the extruded propellants. I have not tried S355, so cannot comment on possible results, but speculate that it would give excellent results as its burning rate would seem to be about right if it is not too bulky to reach its potential in this cartridge. S32l and S335 provide good performance with 500 grain bullets – in the 2200–2300 fps range. Both these propellants are suitable with the lighter 300 grain – 400 grain bullets, and cast bullets. They also have application with reduced velocity loads, where it is desired to replicate .458 Winchester Magnum velocity. S335 is preferable due to its greater bulking factor, and no doubt S355 would be suitable too.

As a matter of interest, highest velocities recorded to date have been achieved with imported propellants. There are many other propellants available overseas within the burning range suitable for this cartridge that have not been tried, but could provide results as good or even improve upon Winchester 748 and Reloader 15. Top velocity achieved with these propellants are 2423 fps and 2425 fps respectively without signs of excessive pressure in the test rifles, using 500 grain bullets. Du Pont IMR 4320 has also proven to be excellent and Norma 203B should provide the expected performance. Somchem’s S355 is similar to IMR 4320 and would likely produce similar excellent results.

Another important consideration is rifle magazine length. Required minimum length for the .450 Ackley is 3.6 inches. Longer than this is desirable allowing greater flexibility of loading. Magazines of 3.8 inches or longer allow bullets to be seated further out providing more powder space and flexibility in loading some of the longer bullets. 500 grain Barnes X bullets are so long that they have to be seated very deeply, thereby greatly reducing capacity and consequently cannot be driven to the higher velocities that this cartridge can achieve with conventional bullets. It is best to stick to .450 grain X bullets in this cartridge, or accept a reduction in velocity with the 500-grain version.

Foremost among the many rifles that can be adapted to this cartridge, are BRNO 602 and CZ550 chambered for .458 Winchester Magnum. A simple chambering job and some important work on the receiver feed rails to ensure reliable functioning of the longer round is all that is required to convert one of these rifles. Front sight height will need changing to bring ‘point of impact’ to ‘point of aim’.

If the original stock is retained it is prudent to rebed and install cross bolts if not provided by the factory, to cope with the increased recoil. Replacing the stock with a laminated stock or a good synthetic version (like the Macmillan), is a wise option.

Any rifle action can be used that provides the required magazine length and bolt travel as a basis for building a custom rifle for this cartridge. P14s have been the basis of many rifles built for the .450 Ackley. Parker Ackley built many of his rifles for this cartridge on these actions that require considerable work to refine into a sporting rifle. Remington 700, Ruger Magnum, Pre 64 M70 Winchester, Super grade M70 Winchester and the many magnum Mauser actions reproduced these days by several rifle makers’ work well for this chambering.

A benefit of using the .375 H&H case is that it allows a magazine capacity greater than with those cartridges based on the .404 and 416 Rigby cases, due to their greater diameters.

Field experience with the .450 Ackley is extensive providing a very satisfactory performance in the hands of many hunters, both amateur and professional. It has been a popular round for use by professional hunters for many years and in fact was only superseded in popularity in recent years by the .458 Lott, with the introduction of factory-made rifles and ammunition. Field results with the Ackley have shown exemplary performance, which would be difficult to improve upon. Penetration with solid bullets is excellent and some results have been astounding. Buffalo shot in the nostril have been penetrated full length with the bullets recovered under the skin of the back leg. Penetration on elephant is sufficient to reach the brain from almost any angle.

In early 1968, we were testing two dart guns developed by a gunsmith in Salisbury, Rhodesia (now Zimbabwe). The gunsmith’s friend, Jeff, had brought a .450 Ackley built on a Magnum Mauser action as backup. This rifle was offered for sale a little while later and unfortunately I could not come up with the asking price of seventy-five pounds (US$150). Two elephant cows were darted with Scoline, a muscle-paralyzing drug working on the respiratory system. Both cows went down after a short run, within about 80 metres of each other. Jeff was tasked with watching the first whilst the rest of the party was examining the second. After a quick examination of the second elephant it was rapidly decided to put them down by shooting. Shouting at Jeff to do so, resulted shortly in a vicious buzzing not too far over our heads. The gunsmith, a heavy-set fellow, ducked involuntarily, and got cramp in his thighs and could not stand straight for a while. This caused a great deal of hilarity among the rest of us. Needless to say we were not amused by Jeff’s carelessness in shooting towards us, which could have resulted in tragedy. He was surprised that the 600-grain Barnes Solid, of the original type made of heavy copper tubing, completely penetrated the cow’s head with considerable remaining velocity to depart over the horizon!

It is stated in “Cartridges of the World”, that the .450 Ackley rifles cannot safely fire .458 Winchester or .458 Lott, because of its bottleneck design and potential head spacing problems. This is absolute nonsense as the method of creating Ackley cases requires fire-forming of cases to fit the chamber when not formed by the manual case-forming operation. Further, all .375 H&H derived cartridges headspace on the belt unless the hand loader elects to headspace on the shoulder to conform to his particular rifle’s chamber dimension by adjusting the sizing die. The .458 Winchester Magnum and .458 Lott lack any form of shoulder and rely entirely on the belt for correct head spacing. A well-know PH in Zimbabwe has a P14-based rifle built for him by the late Parker Ackley, which he has been using for over 30 years. He has fired thousands of .458 Winchester Magnum cartridges through his rifle with completely satisfactory results including using this rifle on a large buffalo cull during the mid 1970s. As soon as he could again obtain Ackley ammunition, he used this and has not had any problems related to chamber erosion from firing so many of the shorter rounds.

The following reloading data is given for information purposes only. Reduce all maximum loads by 10% and work up slowly, watching for any pressure signs. Safe working loads will give extended case life with the components you are using without the primer pockets becoming loose. All dimensions are given in inches and weights in grains. Velocity is given in feet per second. (fps). All cases were made from .375 H&H Magnum brass.







550 Cast gas-check bullets produced 2223 fps using 80 grains of DuPont 3031 which is similar to Somchem’s 335.