IMPROVEMENTS IN GUNS AND GUN PROJECTILES
Year: 1863

page_text: PROVISIONAL SPECIFICATION left by James Chalmers at the Office of the
Commissioners of Patents, with his Petition, on the 30th November
.1863.
I, JAMES CHALMERS, of 5, Wellington Road, Kentish Town, do hereby
declare the nature of the said Invention for "IMPROVEMENTS IN GUNS AND GUN
PROJECTILES," to be as follows:-
This Invention has for its object to facilitate the loading of rifled guns,
prevent windage, reduce friction, and lessen the strain to which the guns are
subjected from the combined action of starting the projectile forward, and
giving it a quick rotary motion simultaneously, and consists of the following
improvements and combinations.
First, the rifling, formed of grooves and lands or ribs of equal or nearly
equal widths to be of the following description:-In describing the grooves,
the depth and width of which may vary with the size of the gun, I take those
suitable for a gun of 8-inch caliber. In this case the grooves and lands or
ribs should be each 12 in number, the grooves about ✓ of an inch deep and
about 1 inch wide. Only one half of the groove to be the full depth, the
other half being bevelled or tapered to the level of the rib, so that there shall
be a square shoulder only on the side of the groove that acts upon and gives
rotation to the shot.
The second improvement consists in adopting a gradually increasing twist
rifling, which will permit the projectile to commence its forward motion at a
slow twist, or the twist may even commence at some distance from the breech,

page_text: in either case gradually increasing till at the muzzle of the gun it attains a
pitch necessary to give the desired rotation to the projectile. I propose for
(say) an 8-inch bore 120 inches in length rifled to commence at the breech
end with a twist of one round in 120 feet gradually changing at the rate of
ten each foot in length, finishing at the muzzle with a twist of one round in
20 feet.
The third improvement consists of an elongated shot, the diameter of which
shall be at the foremost end so as to slide freely into the bore without filling
the grooves. About the middle in the length thereof it shall be reduced in
diameter about one-fourth from thence to the breech end. Close to the
shoulder formed by this reduction shall be cast on or put on a ring of 'soft
brass or other suitable metal, which for an 8-inch shot should be about 1
inches wide, more or less, and equal in outside diameter with the largest or
front part of the shot. Under this ring the shot may be ribbed or roughed to
prevent the ring from turning on the shot. The said ring may be followed
by an iron hoop of similar thickness which will fill up the balance of the
reduced diameter of the shot. The exploding charge acting on the said hoop
will force it forward against the ring of brass, upsetting the ring into the
grooves of the gun. The said ring may also be upset by the explosive, force
of the charge without the hoop, the whole or a portion of the space otherwise
occupied by the hoop being left open to admit the gas or explosive force to act
upon the brass ring, which can in either case be thinned off at the edges V-
shaped or otherwise, and the foremost edge can impinge on a convex shoulder
of the shot less acute in the angle so as more easily to spread or upset the
ring. The force to upset the said ring can be increased or diminished by
altering the thickness of the aforesaid hoop or the size of the opening or open-
ings that communicate between the ring and the charge when no hoop is
used. When great accuracy in firing is required I propose to put on the said
hoop with a draw, so that on being driven forward it may expand slightly at
the breech end by stretching and so coming in contact with the ribs of
the rifling act as a guide. When the shot is to be used in guns with fine
rifling or in guns made of soft metal I propose to cast or put on the said
brass ring of 'less' diameter and greater breadth so as to leave a space to receive
an outer coating of lead over the brass, which shall be roughed to prevent the
lead from turning or stripping off, so that on the upsetting of the brass ring
the lead only may come in contact with the rifling of the gun. The upsetting
of the aforesaid ring in either case at or near the middle of the shot will bring
the weight of the shot to bear on that point, thus comparatively relieving the
other parts of friction and permitting the shot to turn freely with the ring.
1..

page_text: And the pivot nature of the bearing working in the grooves aforesaid will
permit the shot to follow the changing pitch of the increasing twist with less
friction than with a number of bearings, or one long bearing, or in grooves
having square shoulders on each side. The aforesaid shot and grooves with
5 one square shoulder may also be used together or separately with other forms
of rifling.