Polygonal rifling

Polygonal rifling (pəˈlɪɡənəl ) is a type of gun barrel rifling where the traditional sharp-edged "lands and grooves" are replaced by less pronounced "hills and valleys", so the barrel bore has a polygonal (usually hexagonal or octagonal) cross-sectional profile. Polygonal riflings with a larger number of edges have shallower corners, which provide a better gas seal in relatively large diameter bores. For instance, in the pre-Gen 5 Glock pistols, octagonal rifling is used in the large diameter .45 ACP bore, which has an 11.23 mm (0.442 in) diameter, since it resembles a circle more closely than the hexagonal rifling used in smaller diameter bores. The principle of the polygonal barrel was proposed in 1853 by Sir Joseph Whitworth, a prominent British engineer and entrepreneur. Whitworth experimented with cannons using twisted hexagonal barrels instead of traditional round rifled barrels, and patented the design in 1854. In 1856, this concept was demonstrated in a series of experiments using brass howitzers. The British military, however, rejected Whitworth's polygonal designs. Afterwards, Whitworth adopted the concept on small arms, believing that polygonal rifling could be used to create a more accurate rifled musket to replace the Pattern 1853 Enfield. During the American Civil War, Whitworth's polygonally rifled Whitworth rifle was successfully used by the Confederate States Army marksmen (known as the Whitworth Sharpshooters) to terrorize Union Army artillery crews. The muzzle-loading Whitworth rifle is often called the "sharpshooter" because of its superior accuracy compared to other rifled muskets of its era (far surpassing the breechloading Sharps rifle used by the Union Army), and is considered one of the earliest examples of a sniper rifle. The Whitworth sharpshooters killed multiple high-ranking Union officers, most famously Major General John Sedgwick, who was fatally shot at a range of during the Battle of Spotsylvania Court House.