.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
Parent case 7x57 Mauser
Case type rimless bottlenecked [1]
Bullet diameter .257 in (Bad rounding hereScript error mm)
Neck diameter .290 in (Bad rounding hereScript error mm)
Shoulder diameter .430 in (Bad rounding hereScript error mm)
Base diameter .472 in (Bad rounding hereScript error mm)
Rim diameter .473 in (Bad rounding hereScript error mm)
Case length 2.233 in (Bad rounding hereScript error mm)
Overall length 2.775 in (Bad rounding hereScript error mm)
Rifling twist 1-10"
Primer type large rifle
Ballistic performance
Bullet weight/type Velocity Energy
75 gr (Bad rounding hereScript error g) HP3,563 ft/s (Bad rounding hereScript error m/s)2,115 ft·lbf (Bad rounding hereScript error J)
90 gr (Bad rounding hereScript error g) HPBT3,368 ft/s (Bad rounding hereScript error m/s)2,267 ft·lbf (Bad rounding hereScript error J)
100 gr (Bad rounding hereScript error g) SPBT3,108 ft/s (Bad rounding hereScript error m/s)2,145 ft·lbf (Bad rounding hereScript error J)
115 gr (Bad rounding hereScript error g) NOS PART2,777 ft/s (Bad rounding hereScript error m/s)1,970 ft·lbf (Bad rounding hereScript error J)
Source(s): Hodgdon [2]

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 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 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.[3]

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.[4] 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 riflesEdit

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 6.5x50mm 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 6.5mm bullets. The modified Roberts cases are sometimes known as 6.5x.257 Roberts, although the case headstamp may still indicate .257 Roberts.[5] Neither unmodified .257 Roberts ammunition nor the original 6.5x50mm Arisaka ammunition are suitable for firing in rechambered Arisaka rifles.[6]


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 CartridgesEdit

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.[3]

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. [1][7]

P.O. Ackley said that the .257 Roberts Ackley Improved was probably the most useful all-around cartridge.[8] 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 [9] 100 2864 1822
.257 Roberts [1] 100 2898 1865
.257 Roberts (+P) [7] 100 3048 2063
.257 Roberts Ackley Improved [10] 100 3279* 2388*
.25 WSSM [11] 100 3264 2366
.25-06 Remington [12] 100 3283 2394
.257 Weatherby Magnum [13] 100 3512* 2839*
  • using a 26" barrel.

See alsoEdit


  1. 1.0 1.1 1.2 Cartridge info at Accurate Powder
  2. .257 Roberts data at Hodgdon
  3. 3.0 3.1 3.2 The .257 Roberts (.257 Roberts +P) by Chuck Hawks (membership required)
  4. The .257 Roberts by Chuck Hawks
  5. Speer Wildcat Rifle Loads Speer Products Company (1956) p.35
  6. Davis, William C., Jr. Handloading National Rifle Association (1981) ISBN=0-935998-34-9 p.170
  7. 7.0 7.1 .27 Roberts (+P) load data at Accurate Powder
  8. Script error
  9. .250-3000 Savage load data at Accurate Powder
  10. .257 Roberts Ackley Imp Load data at Accurate Powder
  11. .25 WSSM Hodgdon Online Reload data
  12. .25-06 load data at Accurate Powder
  13. .257 Weatherby Magnum load data at Accurate Powder
  • Script error

External linksEdit

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