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SECT. XIV. How to find whether a Piece of Ordnance be true bored, or not.
FIrst, there must be provided a Staff, and two Rammer heads upon the Staff, and on the Rammers heads there must be two right Lines drawn upon them; that is, Divide the two Rammer heads that are the just height, and fit the bore into two equal parts opposite to each other, and draw Lines thereon; the like do by the Staff, that the Lines on the Rammer heads may stand alike, one at one end, and at the other end, as you see in the general Figure LM.
And let the Staff come through one of the Rammer heads about 9 Inches longer than the Cylinder of the Gun; then lay a flat Stick on the Muzzle-Ring, and hold the side of the Quadrant on the Scale to the Stick, and it will by the String and Plummet find the middle, or upper and lower place of the Metal; or by hanging a Plumb-Line and Quadrant before the concave, and the Stick on the top; then after you have found the Point, and upper and lower place of the Metal, put the Rammer head L into the Gun, and let one hold him hard, and right with the Line or Mark on the upper part of the Gun, and lower part with the Line on the Rammer head on the Staff above and below, whilst you put in a Priming Iron in at the Touch-hole, and strike hard the Rammer head, make a Mark; then pull him out, and apply the Line on the Ram∣mer head to the Mark on the upper and lower edge of the Muzzle of the Gun, and you may presently see how much the Mark is from the right Line of the Ram∣mer head, to the right hand, or to the left; that is, if the Mark is just on the right Line, the bore is in the midst: but if you find it a quarter of an Inch on the right or left hand, so much lyeth the bore either to the right or left; and in Shooting, the Piece must be ordred accordingly.
But now to know whether it is thicker upwards or downwards, or how the bore is; the way to know this, find the Diameter of the Piece the Touch-hole, as is already taught in 10 Chap. bend a Wire a little at the very end, that it may catch at the Metal when it is drawn out; after the Wire is fitted thus, first put it into the Touch-hole till it touch the bottom of the Metal in the Chamber; then holding it in that place, make a mark upon the Wire, just even with the said Touch-hole; afterwards draw up the same Wire, untill it catch at the Metal at the top of the Chamber; at that instant make a mark upon the Wire just even with the Touch-hole: the difference betwixt the two marks, is the just wideness of the Chamber, and the distance between the first mark, and the end of the Wire, having half the Diameter of the Chamber of the Piece Sub∣stracted from it, will leave the half of the Diameter of the Piece, if the Piece be true bored; but if this number be more then half the Diameter, then the bore lyeth too far from the Touch-hole, and the upper part of the Metal is thickest; but if less, the under part hath most Metal.
One Example will make it very plain.
Suppose that the Metal at the Britch be represented by ABCD, and the Metal at the Muzzle by efgh, and the bore of the Piece I, whose Centre is l, or the bore K, whose Centre is m: (and I find the Diam. of the Piece to be 21 Inc. at the Touch-hole, the half thereof is 10 ½ inch. Then I find by a Wire the Diam. of the bore to be 5 Inch. but the bottom of the Metal is 8 ½ Inch. half the Diam. of the bore being 2 ½ Inches to a 10 ½ makes 13 to the bottom of the Metal; but if you add to 8½ half the diam. of the bore 2 ½ it is 11, which is half an Inch more than 10½, that shews the Centre of the bore to be at R, and the thinnest of the Metal is undermost, and there he is like to break first; besides, it shews that you must add half an Inch to your Dispert of a true bored Piece, to make a Dispert for the Piece to shoot well: but if you had found by the direction before given, that the ½ an Inch had been less, as 10 only, and the greatest part of the Metal had been under; and therefore you must cut the Dispert ½ an Inch shorter then a Dispert made for such a true bored Piece; and likewise if you find by the Rammer head, and prick with a Wire at the Touch-hole ½ an Inch difference to the right or left hand, as l or m, that side which is the thinnest, you must put the Dispert cut ½ an Inch shorter, the three Figures makes all plain as it is written, as you may see by the direction of inches.