.257 Roberts

Type

Rifle

Place of origin

United States

Production history

Designer

Ned Roberts

Designed

1920s

Manufacturer

Remington Arms

Produced

1934-Present

Variants

.257 Roberts (+P), .257 Roberts Ackley Improved

Specifications

Parent case

7×57mm Mauser

Case type

rimless bottlenecked

Bullet diameter

.257 in (6.5 mm)

Neck diameter

.290 in (7.4 mm)

Shoulder diameter

.430 in (10.9 mm)

Base diameter

.472 in (12.0 mm)

Rim diameter

.473 in (12.0 mm)

Case length

2.233 in (56.7 mm)

Overall length

2.775 in (70.5 mm)

Rifling twist

1-10"

Primer type

large rifle

Ballistic performance

Bullet mass/type	Velocity	Energy
75 gr (5 g) HP	3,450 ft/s (1,050 m/s)	1,983 ft·lbf (2,689 J)
100 gr (6 g) B-TIP	3,020 ft/s (920 m/s)	2,025 ft·lbf (2,746 J)
117 gr (8 g) SPBT	2,840 ft/s (870 m/s)	2,096 ft·lbf (2,842 J)

Test barrel length: 24
Source(s): Accurate Powders

The .257 Roberts also known as .257 Bob is a medium-powered .25 caliber cartridge. 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 not the 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 7×57mm 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 6 mm cartridges such as .243 Winchester and 6mm 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.

Japanese Type 38 Arisaka rifles brought to the United States as wartime souvenirs were sometimes converted by rechambering to utilize more readily available .257 Roberts cartridge cases because commercially produced 6.5×50mm Arisaka cartridges were scarce prior to distribution by Norma Projektilfabrik A/S. The neck of the Roberts case would be slightly enlarged to accept handloaded 6.5 mm bullets. The modified Roberts cases are sometimes known as 6.5×.257 Roberts, although the case headstamp may still indicate .257 Roberts. Neither unmodified .257 Roberts ammunition nor the original 6.5×50mm Arisaka ammunition are suitable for firing in rechambered Arisaka rifles.

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Wikipedia