The projections of the first and second reinforce rings, as well as that of the fillets, are one half of the breadth of the fillet, excepting the fillet at the muzzle, the projcction of which is equal to the whole breadth of the fillet. The projection of the base ring is -1.2g ths of a calibre, and its surface is deteimined by a line touch ing the projections of the first and second reinforce rings.
The vent field is found by placing the centre of the vent field astragal one calibre from the ogee ; the pan extends from the base ring to the fillet of the vent field astragal ; its breadth is two inches, and its projection is determined by a tangent to the swell of the ogee in a direction parallel to the vent field.
The vent is 126- of an inch in diameter, and takes its direction from a point n in the axis, one quarter of a ca libre from the bottom of the bore to the point r, where a line drawn from the bottom of the bore perpendicular to the axis, meets the surface of the pan.
Muzzle.
The length of the muzzle k f is one fifth of thc length of the chase DB, the neck is one third B f, the centre c of the swell is distant one sixth of B f from the face HS ; and the breadth B n of the fillet and astragal is two-thirds of B e.
The diameter of the swell is 33 parts, and so propor tioned to that of the base ring, as to give a dispart of 1'; it is described with a radius r =-} B e, and the hollow at m is described with a radius = 5 c, d ; c d be ing the thickness of the gun at the neck. Lastly, the diameter of the fillet is determinnd by a line drawn through the centre of the swell, parallel to thc axis of the piece. See Plate CCCCXLIII. Fig. 4.
Cascable.
The length k m of the cascable is one calibre and six parts, the diameter p q of the last fillet is one calibre and two parts. The distance of the last fillet to the
centre of the button is 101 parts, and the button is described with a radius of 61 parts, from the centre /'. From the same centre describe an arc with a radius — 113 parts, and another from p with a radius of five parts ; then from their intersection o', and 0 p as a ra dius, describe the arc fi h, which will determine the neck. The ogee h e i is determined by means of the isosceles triangles e f e g h, the sides e f, f e g, g h, being each equal to +iths ofih;ab= 10 parts c d= a 6=2+ parts, a i a b, and n y d. See Fig. 5.
General Ccustruct:on of Brass Guns.
The preceding construction beinf.; understood, there I% ill be no diffirulty in comprehending thc following ge neral principle of construction, although we shall not enter so minutely into particulars.
In general, modern guns are proportioned in length to their calibres, being in one class seventeen, and in the other, dill teen calibres. The guns of seventeen ca libres are 12. 9, 6, and 3 pounders; those of thirteen ca libres are 24, 18, and 12 pounders ; besides which, the 6, 3, and 1 pounders are, as we have seen in the preced ing construction, in some instances, of determinate lengths, without reference to the number of calibres. The weights and lengths of the first class are It will be understood that these constructions apply only to the guns at this time making, or lately made, for the British service ; but we employ a variety of other pieces, which differ very considerably in their lengths and other dimensions ; the principal of which are given in the following table.
Breech. Muzzle.
12, 9, 6, and 3 pdrs. of 17 cal.