BREECHBLOCKS.
The breechblock appears in four distinct types. Our own service has for years used the swinging interrupted screw breechblock which in the 1905 model is the equal of any of that type in existence. The swinging block has serious disadvantages for high angle fire in that it requires an excessive amount of room to operate and is difficult to load at high elevations.
The Italians have introduced a new breechblock in one of their recent guns, consisting of a half cylinder with superimposed spherical face on its cylindrical surface rotating vertically about a horizontal axis perpendicular to the axis of the bore. The gun is loaded through a groove in the breechblock when the latter is in its horizontal position. The block, which is semi-automatic, is very satisfactory. It is adapted to high angle fire.
The French in their “75” have used the rotating eccentric screw type, which is rapid in movement and lends itself fairly well to high angle fire. It is completely enclosed and of rugged construction.
The Germans have used the sliding wedge type of block, moving in a horizontal direction, which does not lend itself to high angle fire.
The United States in its recent field carriage adopted the sliding wedge type in a vertical plane on account of its manifest superiority in fire at high angles. This block is rather difficult to manufacture and the type has a tendency to stick. The automatic closing necessitates a strong closing spring which fatigues the block operator, No. 1 in the gun squad. It is interesting to note that in a prospective new design for the 1916 gun carriage the American Ordnance Department adopted the French breechblock; and the St. Chamond Company, designing for the American Expeditionary Forces, adopted the American drop block.
Requirements for a breech mechanism:
The following may be said to be the principal requirements for a successful breech mechanism.
1. Safety. To be safe: (a) the gas must be restrained from escaping to the rear; this sealing or obturation must be automatic, greater pressure insuring better obturation. (b) The breech of the gun must not be weakened by the fitting of the breech mechanism. (c) The parts must have ample strength to prevent any portion from being blown to the rear. (d) The danger of premature discharge must be minimized. (e) The breechblock must be securely locked to prevent opening on firing.
2. Ease and Rapidity of Working. Otherwise, rapid and continuous fire cannot be maintained. Hence this would include facility in loading and certainty of extraction for rapid fire guns.
3. Not Easily Put Out of Order. In other words it must be able to meet service conditions and hard usage. Parts should have a reserve strength.
4. Ease of Repair. Parts most exposed to wear should be so designed as to permit being replaced. This will also include accessibility to parts, so that breakage of a part will not disable the mechanism for a long time.
5. Interchangeability. Not only should individual parts be made interchangeable by accurate workmanship, but the whole mechanism should be capable of being mounted on similar guns. This is to meet service conditions.