The .276 Pedersen (7×51mm) is an experimental rimless bottlenecked rifle cartridge developed by the United States in the 1920s. It was designed by John Pedersen for use in his semi-automatic T1 rifle. The cartridge features a 7mm bullet (~0.276 inches) and a case length of 51mm.
The primary objective behind the .276 Pedersen was to create a medium-power cartridge that allowed for controllable automatic fire and higher ammunition carrying capacity for soldiers compared to the larger .30-06 Springfield. Its development was part of efforts to modernize U.S. military small arms in the post-World War I period.
Despite showing promise in trials, the .276 Pedersen was ultimately not adopted. The U.S. military decided to retain the .30-06 Springfield due to logistical reasons and the substantial existing stockpile of ammunition. As a result, the T1 rifle and the .276 Pedersen cartridge were eventually shelved, and focus shifted back to improving weapons chambered in the .30-06 Springfield, such as the development of the M1 Garand.