.450 Rigby

In 1993, Paul Roberts (at that time proprietor of John Rigby & Company) was on an elephant hunt in the Zambezi Valley. Both he and his professional hunter, Joseph Wright, were armed with .416 Rigby rifles. An elephant was found and shot, but due to a misjudgment in the distance several more rounds were required to finally bring down the elephant.

After this experience, Paul Roberts felt that a cartridge with a greater bullet weight and a larger caliber would have been more effective in that situation. Once Paul Roberts returned to the United Kingdom he necked up the .416 Rigby case to .458 caliber. The new cartridge fired a .458 in (11.6 mm) bullet weighing 480 gr (31 g) at a velocity of 2378 ft/s (725 m/s) from a 25 in (635 mm) barrel. The new cartridge was named the .450 Rigby in 1994.[2] The cartridge was put into production in 1995. The John Rigby & Co. was building the .416 Rigby rifles on the Magnum Mauser 98 action. Since the .416 Rigby and the .450 Rigby use basically the same case, building rifles for the .450 Rigby was rather simple requiring only a chamber with a modification made in the collar area and a .458 caliber barrel.

The .450 Rigby dimensions and specifications are standardized and governed by the CIP.

CIP compliant .450 Rigby Magnum Rimless cartridge schematic: All dimensions in inches [millimeters].

The CIP recommends a bore diameter of 11.43-millimetre (0.450 in) and a groove diameter of 11.63-millimetre (0.458 in). Barrel will have a 6 grove rifling contour with a twist rate of one revolution in 420 mm (17 in) and a groove width of 3.60-millimetre (0.142 in). CIP specifies a maximum pressure of 4,000 bar (58,000 psi).

Unlike many of the modern .458 caliber dangerous game cartridges like the .458 Winchester Magnum, .458 Lott, or the .460 Weatherby Magnum, the .450 Rigby was designed to operate at more moderate pressures. Maximum pressure limits enforced by CIP is given at 4,000 bar (58,000 psi). At these pressures, the cartridge easily reaches the intended 2,300–2,400 ft/s (700–730 m/s) with the 500-grain (32 g) bullet. The lower pressures provide greater operational reliability in tropical environments where the cartridge is intended for use. Heat can cause higher than normal pressures which can lead to difficulty in extracting the spent case. In a dangerous game hunting situation such failures can result in injury or possibly a fatality.

Unlike the .458 Winchester Magnum and to a degree the .458 Lott, the .450 Rigby reaches the coveted 2,400 ft/s (730 m/s) velocity mark with the 500 gr (32 g) with ease and well under the pressure limits imposed by the CIP upon the cartridge. Handloaders can take advantage of the wide range of .458 caliber (11.6 mm) bullets available. Acceptable bullets weight range from 300-grain (19 g) to 600-grain (39 g). The 500-grain (32 g) bullet can easily reach 2,500 ft/s (760 m/s) and staying within the pressure limitation imposed on the cartridge.[3]

Among commercial sporting cartridges, only the .460 Weatherby Magnum offers a superior performance over the .450 Rigby. However, most bullets manufactured such as those by Hornady and Woodleigh are rated for .450 Rigby velocities rather than those achievable through the .460 Weatherby. For this reason actual performance and penetration on heavy, thick-skinned game species are on par between these two cartridges. The Weatherby cartridge has a 6% greater case capacity than the .450 Rigby but operates at higher pressures.

The .450 Rigby was designed primarily to take heavy, thick-skinned dangerous game animals in Africa. Due to the cartridge’s performance, it would be considered a better cartridge for these game species such as African elephant, Cape buffalo, rhinoceros and perhaps hippopotamus than the usual standby cartridges used on these game such as the .458 Winchester Magnum, or even the .458 Lott cartridges especially if one were to use handloaded ammunition. When hunting these game species a bullet of a tough construction is required especially at the velocities the .450 Rigby is capable of attaining. It is important to tailor the performance to the velocity rating of the bullet with regard to this cartridge as it provides a step up in performance over the cartridges the .458 caliber (11.6 mm) bullets are manufactured for. This is especially true for soft-nosed bullets as they can open up too rapidly at velocities the .450 Rigby can attain. When hunting these game species only bullets weighing 450–600 gr (29–39 g) of a tougher construction should be used.

The .450 Dakota is a variation on the design of the .450 Rigby but predates the latter cartridge by a few years. The Dakota cartridge was designed by Don Allen and is like the .450 Rigby based on the .416 Rigby case necked up to accept a .458 caliber (11.6 mm) bullet. The .450 Dakota is considered a proprietary cartridge, the rights to which are owned by Dakota Arms Inc., Remington Arms Company and the Freedom Group family of companies. Neither the CIP nor SAAMI regulate nor have oversight over this cartridge. While dimensions of the cartridges are similar they are not identical and are not interchangeable due to the shoulder dimensions and the case length. The performance of both cartridges are almost identical. However, Dakota Arms' ammunition is loaded closer to 65,000 psi (4,500 bar).

Schematic of the .450 Dakota. All dimensions in inches [millimeters].

The .450 Dakota launches a 500 gr (32 g) at 2,550 ft/s (780 m/s), a 550 gr (36 g) at 2,450 ft/s (750 m/s) and the 600 gr (39 g) at 2,350 ft/s (720 m/s). While these velocity values are greater than that of the .450 Rigby cartridge, the Dakota ammunition is loaded to near maximum pressure levels while the .450 Rigby is loaded to a pressure level far below the 4,000 bar (58,000 psi) stipulated by the CIP. Given equal pressure level the .450 Rigby will turn out a similar performance level as the .450 Dakota cartridge; this is evident through third-party reloading data provided for the .450 Rigby. Any differences between these cartridges are strictly due to the components use and the pressure levels than due to an actual difference between the cartridges.