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Since cases for the .280 RCBS could be formed by firing .280 Remington ammo in a rifle chambered for the former, Ackley abandoned the 7mm-06 Improved and started chambering rifles for the .280 RCBS. He then changed the 35-degree shoulder to 40-degrees and the .280 Ackley wildcat was born.
Since its dimensions are taken from the 30-06 cartridge from the 1906 US Army cartridge, the lower half of these case dimensions have been used for designing the .243 Winchester, 25-06, .270 Winchester, .280 Remington, 7mm-08, .308, .30-06, .35 Whelen, and others.
The .280 Ackley Improved (.280 AI) was the result of the .280 Remington case modification by P.O Ackley, who pushed out the sidewalls at the shoulder to near parallel and steepened the shoulder angle to 40 degrees in order to increase powder capacity, thus along with increasing the allowable pressure, resulted in increasing the bullet initial velocity by approximately 100 fps.
The .284 Winchester was designed to achieve .270 Winchester and .280 Remington performance from the new Winchester Model 100 autoloader and Winchester Model 88 lever-action rifles. The result was a 7 mm cartridge with about the same overall length as the .308 Winchester but with a wider body, that yields a powder capacity about the same as that ...
The American .280 Remington cartridge is probably the closest ballistic twin of the 7×64mm. When compared to the 7×64mm, the .280 Remington has a slightly lower maximum allowed chamber pressure and as an American 7 mm cartridge has a slightly smaller groove diameter. European 7 mm cartridges all have 7.24 mm (0.285 in) grooves Ø diameter. [6]
The major configuration change for this system was the caliber conversion from 7.62mm NATO (.308 Winchester) to .300 Winchester Magnum to provide soldiers with additional precision engagement capability and range. The contract was for a five-year period with a guaranteed minimum value of $192K and a potential value of up to $28.2 million. [16]
Parker Otto Ackley (May 25, 1903 – August 23, 1989) [1] was an American gunsmith, barrel maker, author, columnist, and wildcat cartridge developer. The Ackley Improved family of wildcat cartridges are designed to be easily made by rechambering existing firearms, and fireforming the ammunition to decrease body taper and increase shoulder angle, resulting in a higher case capacity.
The commercial .280 Remington (or 7mm Express Remington) is very similar, but uses the slightly longer 65 mm 30-03 case with the shoulder headspace extended slightly more than one millimeter (.05 inch) to prevent chambering in .270 Winchester rifles. [17]