|Place of origin||United States|
|Manufacturer||Western Cartridge Company|
|Parent case||.30-06 Springfield|
|Bullet diameter||.264 in (6.7 mm)|
|Neck diameter||.291 in (7.4 mm)|
|Shoulder diameter||.418 in (10.6 mm)|
|Base diameter||.471 in (12.0 mm)|
|Rim diameter||.473 in (12.0 mm)|
|Rim thickness||.049 in (1.2 mm)|
|Case length||2.440 in (62.0 mm)|
|Overall length||3.40 in (86 mm)|
|Rifling twist||1 in 10"|
|Primer type||large rifle|
|Source(s): Newton Arms Company Catalog. 14th edition, 1920. IN Barnes, Frank C. "Cartridges of the World" Digest Books Inc., 1972.|
The .256 Newton was a high-velocity, rimless centerfire cartridge based on the .30-06 Springfield military cartridge and developed in 1913 by Charles Newton in conjunction with the Western Cartridge Company. To make the .256 Newtow cartridge, the .30-06 case was necked down to a caliber of .264 inches, the overall case length was shortened, body taper was increased, the neck was moved back, and the shoulder was given a sharper, 23 degree angle, as opposed to the 17 degree shoulder of the parent cartridge.
The .256 Newton suffered from a lack of available slow burning powders capable of fully exploiting the large capacity of the parent case. Newton's company went bankrupt after the end of World War I and production of commercially loaded ammunition ceased by 1938.
After World War II, with a supply of 6.5mm rifles (.264 caliber), the availability of slower burning powders, and inexpensive, surplus .30-06 brass cases, shooters developed the 6.5mm-06 wildcat cartridge by necking down the .30-06 case to 6.5mm (.264 inches). In 1997, the A-Square company standardized the chambering as the 6.5-06 A-Square with the Sporting Arms and Ammunition Manufacturers' Institute (SAAMI). Although substantially similar, the .256 Newton is not interchangeable with the .30-06 parent cartridge, the 6.5-06 wildcat chambering, or the SAAMI standardized 6.5-06 A-Square cartridge.
- Barnes, Frank, and Amber, John T. Cartridgs of the World (DBI, 1972), p.76, ".256 Newton".
- ".256 Newton and 6.5-06". Terminal Ballistics Research. Terminal Ballistics Research. Retrieved 22 March 2018.
- "SAAMI 6_5-06 A-Square" (PDF). Sporting Arms and Ammunition Manufacturers' Institute. SAAMI. Archived from the original (PDF) on 2018-03-22. Retrieved 22 March 2018.
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