but were not satisfactory so studded projectiles were adopted. However, these did not seal the gap between shell and barrel. Wads at the shell base were also tried without success. In 1878, the British adopted a copper "gas-check" at the base of their studded projectiles and in 1879 tried a rotating gas check to replace the studs, leading to the 1881 automatic gas-check. This was soon followed by the Vavaseur copper driving band as part of the projectile. The driving band rotated the projectile, centered it in the bore and prevented gas escaping forwards. A driving band has to be soft but tough enough to prevent stripping by rotational and engraving stresses. Copper is generally most suitable but cupronickel or gilding metal were also used. Percussion fuze Although an early percussion fuze appeared in 1650 that used a flint to create sparks to ignite the powder, the shell had to fall in a particular way for this to work and this did not work with spherical projectiles. An additional problem was finding a suitably stable "percussion powder". Progress was not possible until the discovery of mercury fulminate in 1800, leading to priming mixtures for small arms patented by the Rev Alexander Forsyth, and the copper percussion cap in 1818. The percussion fuze was adopted by Britain in 1842. Many designs were jointly examined by the army and navy, but were unsatisfactory, probably because of the safety and arming features. However, in 1846 the design by Quartermaster Freeburn of the Royal Artillery was adopted by the army. It was a wooden fuze about 6 inches long and used shear wire to hold blocks between the fuze magazine and a burning match. The match was ignited by propellant flash and the shear wire broke on impact. A British naval percussion fuze made of metal did not appear until 1861. Types of fuzes Percussion fuzes Direct action fuzes Graze fuzes Delay fuzes Base fuzes Airburst fuzes Time fuzes Proximity fuzes Distance measuring fuzes Electronic time fuzes Smokeless powders Gunpowder was used as the only form of explosive up until the end of the 19th century. Guns using black powder ammunition would have their view obscured by a huge cloud of smoke and concealed shooters were given away by a cloud of smoke over the firing position. Guncotton, a nitrocellulose-based material, was discovered by Swiss chemist Christian Friedrich Schönbein in 1846. He promoted its