The .257 Roberts, The Most Useful Round that I have ever used on the range or in the Field!

.257 Roberts
257 Roberts.JPG
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
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 [1]

The .257 Roberts also known as .257 Bob [2] is a medium-powered .25 calibercartridge. 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.[3]


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.[4]
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.[5] Today, although overshadowed by other cartridges, it lives on with bolt-action rifles being available from some major manufacturers.

Conversion of war-souvenir Japanese Arisaka rifles[edit]

Japanese Type 38 Arisaka rifles brought to the United States as wartime souvenirswere sometimes converted by rechambering to utilize more readily available .257 Roberts cartridge cases because commercially produced 6.5×50mm Arisakacartridges 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.[6] Neither unmodified .257 Roberts ammunition nor the original 6.5×50mm Arisaka ammunition are suitable for firing in rechambered Arisaka rifles.[7]


With light bullets the .257 produces little recoil and has a flat trajectory suitable for varmint hunting. With heavier bullets it is 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.

Improved cartridges[edit]

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.[4]
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.[8]
P.O. Ackley said that the .257 Roberts Ackley Improved was probably the most useful all-around cartridge.[9] 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.


Quick .25 caliber comparison chart
cartridge Bullet Weight Muzzle Velocity (ft/sec) Muzzle Energy (ft·lbf)
.250-3000 Savage [10] 100 2911* 1882*
.257 Roberts [1] 100 3020 2025
.257 Roberts (+P) [1] 100 3090 2120
.257 Roberts Ackley Improved [11] 100 3226 2311
.25 WSSM [1] 100 3313 2438
.25-06 Remington [1] 100 3324 2454
.257 Weatherby Magnum [1] 100 3512** 2739**
6.5×55mm [12] 100 3183 2250

Using a 24″ barrel except:

* using a 22" barrel.
** using a 26" barrel.

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