.270 Winchester

The .270 Winchester is a rifle cartridge developed by Winchester Repeating Arms Company in 1923, and it was unveiled in 1925 as a chambering for their bolt-action Model 54 to become arguably the flattest shooting cartridge of its day, only competing with the .300 Holland & Holland Magnum, also introduced in the same year. The .270 Winchester case is a necked down .30-03 Springfield, retaining the slightly longer neck of that original parent cartridge. (Note the actual SAAMI and CIP length specifications of the .270 Winchester vs. the .30-06 Springfield and that of their parent cartridge the .30-03 Springfield, with a C.I.P. length of 64.52mm, and a SAAMI of 2.540 inches. Winchester had chambered the Model 1895 Lever Action Rifle in .30-03 Springfield in 1905, then the slightly shorter .30-06 Springfield in 1908.) The .270 Winchester uses a .270 inch (6.86 mm) bore diameter and a .277 inch (7.04 mm) bullet diameter. The bore diameter was likely inspired by 7mm Mauser. The physics of lead projectiles determines that .277in. bullets of a similar material and weight to the .308in. bullet (commonly used in the .30-06 Springfield) will obviously have to be longer than that similar weight .308in. lead projectile. As an example compare bullets of the same weight but different calibers. The 150gr. .277 caliber bullet is longer and has a higher sectional density vs. the ballistically significant shorter length and lower sectional density of a 150gr. .308 caliber bullet. The use of the longer cartridge case neck was a design element to complement those longer bullets with better sectional density.