The CHASE is the conical part of the gun in front of the reinforce.
The ASTRAGAL AND FILLETS in field guns, and the chase ring in other pieces, are the mouldings at the front end of the chase.
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The NECK is the smallest part of the piece in front of the astragal or the chase ring.
The SWELL OF THE MUZZLE is the largest part of gun in front of the neck. It is terminated by the muzzle mouldings, which in field and siege guns, consist of the lip and fillet. In sea-coast guns and heavy howitzers and columbiads, there is no fillet. In field and siege howitzers, and in mortars, a muzzle-band takes the place of the swell of the muzzle.
The FACE of the piece is the terminating plane perpendicular to the axis of the bore.
The TRUNNIONS are cylinders, the axes of which are in a line perpendicular to the axis of the bore, and in the same plane with that axis.
The RIMBASES are short cylinders uniting the trunnions with the body of the gun. The ends of the rimbases, or the shoulders of the trunnions, are planes perpendicular to the axis of the trunnions.
The BORE of the piece includes all the part bored out, viz.: the cylinder, the chamber (if there is one), and the conical or spherical surface connecting them.
The CHAMBER in howitzers, columbiads, and mortars, is the smallest part of the bore, and contains the charge of powder. In the howitzers and columbiads,[1] the chamber is cylindrical; and is united with the large cylinder of the bore by a conical surface; the angles of intersection of this conical surface with the cylinders of the bore and chamber, are rounded (in profile) by arcs of circles. In the 8-inch siege howitzer, the chamber is united with the cylinder of the bore by a Spherical surface, in order that the shell may when necessary, be inserted without a sabot.