The following is for cannons and the like, but does anyone know what type of plug bore was used:
"The Cylinder Gauge is a hollow cylinder of cast or wrought iron turned to the exact minimum or true diameter of the bore. Its length is equal to its diameter, and it has at each end cross-heads perpendicular to each other. In one of the cross --heads, and in the axis of the cylinder, a smooth hole is left of the size of the cylinder staff. At the other end the hole is threaded for the reception of the end of the cylinder staff, on which the gauge is now screwed, and this pushed slowly to the bottom of the bore. It must go all the way down, or the bore is too small; but if it goes down, the bore may still be too large, and irregular in its dimensions.
Star Gauge Figs. 40 and 41, Pl. 11. – To ascertain this, a more complicated and delicate instrument is used, called the star gauge from the shape of its head, which is of brass, with four steel sockets, two movable and two stationary, for the measuring points. There are four measuring points for each calibre; and when two of these are screwed into the fixed sockets, the distance between their points is equal to the true diameter of the bore. The movable sockets rest against the inclined sides of a slider or wedge whose sides incline 0.35 in. in a length of 2.2 in., so that by pushing the slider the 35th part of this distance (about 0.06 in.) the distance between the two sockets or the measuring points, if screwed into their places, is increased .01 in. The slider is fastened to a square steel rod consisting of three parts, which are screwed together according to the length of bore to be measured. This rod passes through a brass tube which is also made in three parts, and to screw together. This tube is graduated into inches and quarter inches, commencing at the plane of the measuring points, so as to indicate the distance of these from the muzzle of the gun.
The handle, Fig. 41, Pl. 10, is of wood, attached to a brass cylinder or socket through which the rod passes into the handle. The socket of the handle slips over the end of the brass tube made smaller for the purpose, and has a slit in it allowing the brass tube to be seen through. On the side of this slit a scale is constructed, to indicate the movement of the measuring points. Each joint of the long tube has a mark on it, to show the position for the zero of the scale when the instrument is properly adjusted for any particular calibre. In this position the handle is fixed to the sliding rod by means of a screw clamp." from
http://www.usregulars.com/gibbons/gibbons_chapter_ii.htm about 3/4s of the way down the page.
Kind Regards,
Raimey
rse
