6.5 mm - 257 Roberts
October 31, 2014
Recently I came across a 1960s era Herters die set at a yard sale. The dies were made to reload a once popular wildcat cartridge, the 6.5 millimeter 257 Roberts. Really nothing more than the 257 Roberts case necked up to 6.5 millimeter, this wildcat cartridge found an unexpected niche from the influx of Japanese Arisaka rifles flooding onto the U.S. Market after World War 2.
The 6.5 mm - 257 Roberts
Derived from the 98 Mauser action, tens of thousands of sturdy and bargain priced Arisaka rifles were imported into this Country. Unfortunately at the time there was a dearth of available military surplus ammunition and really nothing in the way of available brass or soft point hunting loads for 6.5 mm Arisaka .
The remedy for this lack of available ammunition was to rechamber them to the 6.5mm - 257 Roberts.
With a rim diameter equal to the 6.5 Arisaka cartridge, it was found that this 6.5-257 Roberts was an easy conversion requiring only the use of a chamber reamer to enlarge the chamber to the size of the new case. No alterations were required to the bolt face, extractor, barrel or magazine.
| 6.5 Arisaka | 6.5mm- 257 Roberts | |
|---|---|---|
| Bullet Dia (inches) | 0.264 | 0.264 |
| Rim Dia. (inches) | 0.471 | 0.467 |
| Case Len (inches) | 2.00 | 2.233 |
Before running 257 brass in the resizing die, it is necessary to bell the mouth of the case first. The Lee Universal case expanding die works well for this.
257 Roberts is a wildcat cartridge based on a necked down 7mm mauser case. Developed and marketed by Remington arms in 1934 (de Haas, 35) . The 257 Roberts became a popular big game cartridge in the 1940s and 50s
de Haas, Frank "Bolt Action Rifles 1984 p. 96
Barnes, Frank "Cartridges of the World 9th Ed." p. 174