A steel point
is screwed on to the end. When pushed to the bottom of the bore, the
staff coincides very nearly with its axis. The outer joint is
graduated to inches and tenths. A slide is made to play upon it with a
vernier scale, graduated to hundredths of an inch. On the inner end of
the slide a branch projects at a right angle, sufficiently long to
reach across the muzzle face, and, when in contact with it, to
indicate the precise length obtained from that point to the end of the
measuring-point on the other end of the staff. A half disk of wood,
made to fit the bore, with a groove for the staff to rest in, placed
just inside of the muzzle, is useful in preventing any springing of
the staff.

The point being taken off, the staff can be used with the cylinder
gauge, to measure the distance to which the latter descends. But as
the graduation is intended for the points, care must be taken in this
case to allow for the difference.

5th. A chamber-gauge for verifying the shape and size of conical
chambers.

The head should be made of close-grained, well-seasoned wood, and of
the exact dimensions of the chamber. Two planes, crossing each other
at a right angle, coinciding with the vertical and horizontal central
sections, have been found better than a solid block. The edges should
be bevelled. A metal socket in its centre connects it with the
measuring-staff. Being pushed to the bottom of the bore, if the length
coincides with that obtained by the point, it is obvious that the
chamber is large enough, provided the cylindrical part has not been
bored too deep, in which case a shoulder would be found at the
junction. The edges of the gauge should be chalked before it is
inserted. When withdrawn, if the chalk-marks are visible all around
the chamber, it is evident the chamber is not too large. With slight
modifications, this arrangement may be applied to the slope of
cylindrical chambers, and to the curve at the bottom of the bore of
any guns. Should the inspection of guns with conical chambers or
slopes take place at the foundry, an examination of the chamber reamer
will be very satisfactory. If found correct in size and shape, the
impossibility of making the chamber too large will be apparent.

6th. A star-gauge, for measuring the diameters of the bores and of
cylindrical chambers. This instrument is composed of the staff, the
handle, and a set of points for each calibre.

The staff is a brass tube, made in three pi