.256 Newton

.256 Newton
Place of originUnited States
Production history
DesignerCharles Newton
ManufacturerWestern Cartridge Company
Parent case.30-06 Springfield
Case typeRimless
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 length2.440 in (62.0 mm)
Overall length3.40 in (86 mm)
Rifling twist1 in 10"
Primer typelarge rifle
Ballistic performance
Bullet mass/type Velocity Energy
123 gr (8 g) 3,103 ft/s (946 m/s) 2,632 ft⋅lbf (3,569 J)
140 gr (9 g) 3,000 ft/s (910 m/s) 2,800 ft⋅lbf (3,800 J)
Source(s): Newton Arms Company Catalog. 14th ion, 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.[1] To make the .256 Newton 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.[2]

The .256 Newton suffered from a lack of available slow burning powders capable of fully exploiting the large capacity of the parent case.[2] Newton's company went bankrupt after the end of World War I and production of commercially loaded ammunition ceased by 1938.[2]

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).[2] 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).[2][3] 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.[2]


  1. ^ Barnes, Frank, and Amber, John T. Cartridges of the World (DBI, 1972), p.76, ".256 Newton".
  2. ^ a b c d e f ".256 Newton and 6.5-06". Terminal Ballistics Research. Terminal Ballistics Research. Retrieved 22 March 2018.
  3. ^ "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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