From Wikipedia, the free encyclopedia:
"The .257 Roberts a medium powered .25 caliber cartridge known affectionately as the Bob. It has been described as the best compromise between the low recoil and flat trajectory of smaller calibers such as the .22 and 6mm, and the strong energy but strong recoil of larger popular hunting calibers, such as the 7mm family and the popular .30-06.
Many cartridge designers in the 1920s were creating various .25 caliber cartridges. Because of its size, the 7x57mm Mauser case was a common choice, having near the ideal volume capacity for the "quarter-bore" (called this because the .25 caliber is one quarter of an inch) using powders available at that time. Ned Roberts is usually credited with being the designer for this cartridge idea. Eventually in 1934 Remington Arms chose to introduce their own commercial version of such a cartridge, and although it wasn't the exact dimensions of the wildcat made by Roberts, they called it the .257 Roberts.
From its introduction until the appearance of more popular 6mm cartridges such as .243 Winchester and 6 mm Remington), it was a very popular general purpose cartridge. Today, although overshadowed by other cartridges, it lives on with bolt-action rifles being available from some major manufacturers.
One of the less well known but nonetheless common rifles commonly found chambered in .257 Roberts is the Japanese Type 38 Arisaka, which was often converted to the more readily available domestic cartridge due to the relative unavailability of commercially produced 6.5x50mm Arisaka Japanese cartridges in post-World War II America.
With light bullets the .257 produces little recoil and has a flat trajectory suitable for varmint hunting. With heavier bullets it’s capable of taking all but the largest North American game animals. The original factory load for this is very similar to the .250-3000 Savage.
Remington introduced the commercial version of this popular wildcat as a low-pressure round. At the time there were many older actions available of questionable strength. With a modern action and handloading, this cartridge is capable of markedly improved performance.
One of the common improvements is called the .257 Roberts(+P) which has a SAAMI maximum pressure limit of 58,000 PSI compared to the 54,000 PSI listed for the standard .257 Roberts. P.O. Ackley said that the .257 Roberts Ackley Improved was probably the most useful all-around cartridge. The Ackley Improved was a typical change of a steeper shoulder coupled with blown-out sides for more of a straight cartridge, providing greater powder capacity."
.257 Roberts. (2009. March 1). In Wikipedia, The Free Encyclopedia. Retrieved 17:27. March 17. 2009. from http://en.wikipedia.org/w/index.php?title=.257_Roberts&oldid=274132624