At a specified distance from the base of the shell a groove or band-score is turned for the rotation band. For projectiles under 7-inches calibre, pure copper is usually employed, but for larger calibre an alloy of 97-1/2 per cent of pure copper and 2-1/2 per cent of nickel is used and is annealed before banding. The rough bands are in a form of solid rings cut from drawn tubes or cylindrical castings, and must be carefully hammered into the score or preferably pressed in by hydraulic pressure and finally turned to proper size, shape, and finish. Their use has been previously described and the improvements in armor-piercing shells hereinafter described are based upon a study of the stresses sustained by a projectile upon impact while rotating about its major axis at the high rotative velocity which the engaging of these bands with the rifling of the gun has imparted to the shell. The following table compiled by the author gives the rotative velocities of various projectiles: -------+----------+----------+-------+-------+------+------------ | | | | | Muz. | | | | | | Engy.| Calibre|Wt., lbs. | Muz. Vel.| | | Ft. | Type of Inches |Projectile| Ft. Secs.| R.P.S.| R.P.M.| Tons | Gun -------+----------+----------+-------+-------+------+------------ 3 | 12 | 870 | 139 | 8,340| 63 |Hotchkiss 3.2 | 13.5 | 1,685 | 253 | 15,180| 266 |Field '90 3.6 | 20 | 1,550 | 206 | 12,360| 333 | " 1891 3.6 | 20 | 650 | 86 | 5,160| 59 |Mortar 1890 5 | 45 | 1,830 | 176 | 9,560|1,045 |Siege 1890 7 | 105 | 1,085 | 76 | 4,560| 853 |Howitzer '90 7 | 125 | 690 | 49 | 2,940| 412 |Mortar '92 -------+----------+----------+-------+-------+------+------------ U.S. SEA-COAST LAND SERVICE GUNS -------+----------+----------+-------+-------+--------+---------- | | | | | Muz. | | | | | | Engy. | Calibre|Wt., lbs. | Muz. Vel.| | | Ft. | Type of Inches |Projectile| Ft. Secs.| R.P.S.| R.P.M.| Tons | Gun -------+----------+----------+-------+-------+--------+---------- 8 | 300 | 1,950 | 111 | 6,660 | 7,907 | 1888M 10 | 575 | 1,975 | 95 | 5,700 | 15,548 | 1888M 12 | 1,000 | 2,100 | 84 | 5,040 | 30,750 | 1902 16 | 2,370 | 1,975 | 59 | 3,540 | 64,084 | -------+----------+----------+-------+-------+--------+---------- KRUPP GUNS