.276 Pedersen

.276 Pedersen
En-bloc clip loaded with 10 rounds of .276 Pedersen. Image from John Pedersen patent.
Type	Rifle
Place of origin	United States
Service history
In service	1923–1932 (experimental)
Used by	United States
Production history
Designer	John Pedersen
Designed	1923
Specifications
Case type	Rimless, bottleneck
Bullet diameter	.2842 in (7.22 mm)
Neck diameter	.313 in (8.0 mm)
Shoulder diameter	.385 in (9.8 mm)
Base diameter	.450 in (11.4 mm)
Rim diameter	.450 in (11.4 mm)
Case length	2.023 in (51.4 mm)
Overall length	2.855 in (72.5 mm)
Primer type	Large rifle

The .276 Pedersen (7×51mm) round was an experimental 7 mm cartridge developed for the U.S. Army and used in the Pedersen rifle and early versions of what would become the M1 Garand.

Developed in 1923 in the United States, it was intended to replace the .30-06 Springfield in new semi-automatic rifles and machine guns. When first recommended for adoption, M1 Garand rifles were chambered for the .276 Pedersen, which held ten rounds in its unique en-bloc clips. The .276 Pedersen was a shorter, lighter and lower pressure round than the .30-06, which made the design of an autoloading rifle easier than the long, powerful .30-06. The U.S. Army Chief of Staff Gen. Douglas MacArthur rejected the .276 Pedersen Garand in 1932 after verifying that a .30-06 version was feasible.

Pedersen's round fired a 0.284-inch (7mm) bullet. Comparable to the contemporary Italian 6.5×52mm (0.268 in) Carcano or the Japanese 6.5mm (0.264 in) Arisaka, it produced velocities of around 2,400 feet per second (730 m/s) with 140 or 150 grain (9.1 or 9.7 g) projectiles. The case was two inches (51 mm) long with significant taper. Tapered cases require the use of highly curved magazines similar to the Kalashnikov, although for the short magazines of the Pedersen and Garand rifles, this was immaterial. Both waxed and bare cartridges were made for the Pedersen and Garand rifle respectively. An armor-piercing T1 cartridge was developed and presumably a tracer.

At the time of its introduction, the .276 Pedersen was a solution to a significant problem. The U.S. Army wanted a general issue autoloading rifle that would fire the .30-06 cartridge, but such a rifle was prohibitively large with existing designs such as the Browning Automatic Rifle and French Chauchat. A weapon of the same weight as the M1903 needed to fire a smaller cartridge. Pedersen's cartridge was viewed as a compromise as it was underpowered compared to most military rifle cartridges. This decreased recoil energy made possible a reliable, lightweight semi-automatic rifle with existing technology. Despite overcoming these early semi-automatic problems, the Garand was chosen because it did not require the use of lubricated cartridge cases for reliable function. The Garand was originally going to be chambered in the .276 Pedersen, but the logistics of changing all of the infantry's guns (including machine guns) to a new round was judged cost-prohibitive, so the Garand was chambered in .30-06, removing the need for the new cartridge.