.257 Roberts

.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, bottleneck
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 [1]

The .257 Roberts, also known as .257 Bob,^[2] is a medium-powered .25 caliber rifle cartridge. It has been described as the best compromise between the low recoil and flat trajectory of smaller calibers such as the 5 mm (.22 in) and 6 mm (.24 in), and has more energy, but is harder recoiling, similar to larger hunting calibers, such as the 7 mm (.28 in) and 7.62 mm (.30 in).^[3]

Nominal bullet diameter of the .257 Roberts is .257 inches. The .257 Roberts uses the same caliber bullets as .250 Savage or the more powerful .25-06 Remington. Barrel rifling diameter, from which calibers derive their designations, is 0.250 in or 6.35 mm.