lit by the flash through the windage between the shell and the barrel. At about this time, shells began to be employed for horizontal fire from howitzers with a small propelling charge and, in 1779, experiments demonstrated that they could be used from guns with heavier charges. The use of exploding shells from field artillery became relatively commonplace from early in the 19th century. Until the mid 19th century, shells remained as simple exploding spheres that used gunpowder, set off by a slow burning fuse. They were usually made of cast iron, but bronze, lead, brass and even glass shell casings were experimented with. The word bomb encompassed them at the time, as heard in the lyrics of The Star-Spangled Banner ("the bombs bursting in air"), although today that sense of bomb is obsolete. Typically, the thickness of the metal body was about a sixth of their diameter, and they were about two-thirds the weight of solid shot of the same caliber. To ensure that shells were loaded with their fuses toward the muzzle, they were attached to wooden bottoms called sabots. In 1819, a committee of British artillery officers recognized that they were essential stores and in 1830 Britain standardized sabot thickness as a half-inch. The sabot was also intended to reduce jamming during loading. Despite the use of exploding shells, the use of smoothbore cannons firing spherical projectiles of shot remained the dominant artillery method until the 1850s. Modern shell The mid–19th century saw a revolution in artillery, with the introduction of the first practical rifled breech loading weapons. The new methods resulted in the reshaping of the spherical shell into its modern recognizable cylindro-conoidal form. This shape greatly improved the in-flight stability of the projectile and meant that the primitive time fuzes could be replaced with the percussion fuze situated in the nose of the shell. The new shape also meant that further, armor-piercing designs could be used. During the 20th century, shells became increasingly streamlined. In World War I, ogives were typically two circular radius head (crh) – the curve was a segment of a circle having a radius of twice the shell caliber. After that war, ogive shapes became more complex and elongated. From the 1960s, higher quality steels were introduced by some countries for their HE shells, this enabled thinner shell walls with less weight of metal and hence a greater weight of explosive.