THE THIRD EPOCH (1885 TO THE.PRESENT.DAY) This period may be distinguished as the steel era of high velocity guns. The epoch begins with the advent of smokeless propellents (cordite, q.v.). The much greater gas yield effi ciency of these permitted of lighter charges or higher velocities and required longer and stronger guns for the suitable combustion of the slower burning high pressure powders. (The 68-pounder was fired with 18 lb. of gun powder and gave a muzzle velocity of i,ioo f.s., whereas the loo lb. projectile fired with 144 lb. of cordite had a muzzle velocity of 2,63o f.s.) By 1890 nitro cellu lose and nitro-glycerine powders (so-called, but in the usual form cords or small cylinders) had generally replaced gun powder in the ordnance of all first class powers. The ordnance developments of this epoch are as remarkable as those of the preceding one, but the advances have been due to the great progress in metallurgical knowledge and practice, in engineering science, and in the technique of construction, rather than to radical innovations such as those for which the previous epoch was conspicuous. This era is notable for the steady advance in the power of guns through the increase in calibre and hence in the weight of the projectile, and increase in muzzle velocity; also for the development in automatic machine guns and semi-auto matic quick-firing guns.
being in a bag such guns are called "bag guns" in U.S.A. In the Q.F. gun obturation is effected, as in a rifle and shot gun, by the expansion of the metal cartridge case which contains the pro pellent. Such guns are called "case guns" in the U.S.A. If the projectile is attached to the cartridge case, forming one loading unit, the ammunition is called "fixed" to distinguish it from the "separate" type.
Various systems of wire construction had already been put for ward during the preceding epoch.
It is noteworthy that Germany adhered throughout to an "all steel" construction and preferred a Q.F. mechanism for all natures of guns. In the Krupp gun of medium and heavy calibre a hoop form of construction is used in preference to tubes. Since the World War an "all steel" construction for medium calibre guns is more general in view of the greatly improved properties of high grade alloy steels. For smaller guns a monobloc form of construction is sometimes preferred, owing to the success of a