Complex sentence: 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.
Split into simpler sentences: The.276 Pedersen (7 × 51mm) round was an experimental 7 mm cartridge developed for the United States Army. It was used in the Pedersen rifle and early versions of what would become the M1 Garand.