.257 Roberts
The .257 Roberts, also known as .257 Bob, 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).
| .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 | ||||||||||||||||
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| Test barrel length: 24 Source(s): Accurate Powders | ||||||||||||||||
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.
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