The Armstrong breech-loader is no longer manufactured, but there are many guns of this type in service. These breech-loaders were originally of two types, known as the screw and the wedge gun. The latter was designed especially for naval use, but it has been entirely withdrawn from service, leaving only the screw type. It is not improbable that another type of breech-loaders will eventually find its way into service, having a breech-closing arrangement similar to the French type in principle. [Illustration: 64-pdr.] [Illustration: SECTION OF GROOVE FULL SIZE. French Groove.] [Illustration: French Modified Groove.] [Illustration: Woolwich Groove.] [Illustration: Plain Groove.] Various systems of grooves will be found in these guns, corresponding to different stages of development. In the 7-pdr. the French groove is used, having sharp angles, the loading side being at a sharper pitch than the driving. In the 9-pdrs. appears the modified French groove, in which the angles are rounded off and the loading side is at right angles to the driving side. In the 64-pdr. converted gun the plain groove is used. This groove is almost rectangular, the driving side being canted but little. In the 64-pdr. of 64 cwt. the shunt groove is used. This is a double groove, one half being deeper than the other, the rear end of the groove having a shunt by which the studs are turned into the shallow half. The 7-inch muzzle-loaders have the Woolwich groove with a uniform twist. This groove is the final modification of the original French groove. The higher calibres up to the 16-inch gun have the Woolwich groove with an increasing twist. The 16-inch calibre will have the plain multigroove, or the groove ordinarily used for expanding projectiles. The breech-loaders have the Armstrong multigroove, a groove which in section is not unlike a saw-tooth. _7-pdr. Steel R. M. L. 200 lbs._ Introduced into service in 1873. Made of a single block of steel, having no swell at the muzzle, but a small dispart patch into which the fore sight screws. Copper vent bouch. The sight is a plain, centre hind sight set at a permanent angle of deflection of 3°. It seats in a hole bored in the metal of the gun, having a simple clamp-screw to hold it in position. Two sight-bars are used with the gun, one graduated to 6° and the other to 12°, the graduations on both being for intervals of 3´. This gun may be distinguished from the 9-pdr. by the slope at the junction of the reinforce and chase, which is gradual. _9-pdr. Wrought Iron R. M. L. 6 and 8 cwt._