The information below is from:
http://www.accuratepowder.com/data/PerCaliber2Guide/Rifle/Standarddata(Rifle)/243Cal(6.17mm)/6mm%20Remington%20pages%20207%20and%20208.pdfIntroduced by Remington in 1955 as the .244 Remington, this cartridge was chambered in the Model 722 bolt action and later in the Model 760 slide action rifles. The .244/
6mm Remington is based on the .257 Roberts case necked down to .24 caliber and was originally a wildcat cartridge credited to RCBS’s Fred Huntington.
When originally introduced, .244 Remington rifles were made with 12-inch twist barrels since Remington intended it to be only a varmint cartridge. This assumed, incorrectly, the shooting public would agree with them. Since the .243 Winchester would accurately shoot heavier bullets, it quickly became a legitimate deer cartridge and soon caused the demise of the ballistically superior .244 Remington.
In order to correct the situation, Remington renamed the cartridge and introduced new rifles with 9-inch twist barrels.
The SAAMI Maximum Average Pressure for the 6mm Remington is 65,000 P.S.I. This is nearly 10% higher than the pressure limit for the .243 Winchester. This fact, coupled with the increased case capacity of the 6mm Remington, allows greater flexibility for the handloader.
The information below is from:
http://www.accuratepowder.com/data/PerCaliber2Guide/Rifle/Standarddata(Rifle)/284Cal(7.21mm)/280%20Remington%207mmExpress%20pages%20244%20and%20245.pdfOriginally introduced in 1957 to compete with the .270 Winchester, the .280 Remington is another derivative of the .30-06. It is very similar to the wildcat 7mm-06. The .280 is available in auto loading, pump action, and bolt action rifles.
After it failed to dislodge the popular .270 Winchester, the .280 was renamed “7mm Express.” Apparent confusion between it and the popular 7mm Remington Magnum caused the company to revert back to the original .280 Remington moniker.
When loaded to similar pressures, the .280 Remington duplicates or exceeds the performance of the .270 Winchester on both varmints and big game. This is an excellent cartridge for the handloader, handling a wide variety of bullet weights with ease.
The SAAMI Maximum Average Pressure for the .280 Remington/7mm Express is now established as 60,000 P.S.I. and 50,000 C.U.P.
yooper77
I feel the 244 Remington/6mm Remington and the 243 Winchester cartridges are perfect, but to pick one over the other, I would choose the 243 Winchester without hesitation.
I never did understand the confusion with the any cartridge names. How could anyone confuse the 7mm Express Remington with the 7mm Remington Magnum?