Chapter VIII: 75-Mm Field Gun Model 1917 (british)

Weights and Dimensions.

Weight 995 lbs.
Caliber 2.95 in.
Total length 88.21 in.
Length of bore 83.915 in.
Length of rifled portion 72.72 in.
Rifling 24 grooves, right hand twist, zero turns at the origin
to 1 turn in 75 in. (25.4 calibers) at 9.72 in. from the
muzzle thence uniform.

The Carriage.

Weight of carriage, complete 1950 lbs.
Weight of gun and carriage complete 2945 lbs.
Weight at end of trail carriage limbered 96 lbs.
Diameter of wheels 56 in.
Width of track 60 in.
Length of recoil 49 in.
Maximum angle of elevation 16 degrees
Maximum angle of depression 5 degrees
Maximum amount of traverse of gun on the carriage 142 mils

DESCRIPTION.

_The gun_ is a combination of a built up and a wire wrapped gun. It consists of a tube, a series of layers of steel wire, jacket and breech ring. The tube extends from the rear end of the chamber to the muzzle. Over the rear portion of the tube are wound 15 layers of O.04 by O.25” steel wire. The jacket is fitted over the wire and the tube, and is secured longitudinally by corresponding shoulders and the breech ring, which is screwed over the jacket at the rear, and secured by a set screw. The breech ring is prepared for the reception of the breech mechanism, and is provided on the upper side with a lug for the attachment of the hydraulic buffer.

_Breech Mechanism Assembled_]

_The breechblock_ is of the swinging type, interrupted screw with two threaded and two slotted sectors instead of the four we are familiar with in the 3”. The firing mechanism is of the continuous pull type.

The ammunition used is similar to that used with the American and French types of 75s.

=The Principal Parts of the Carriage are=:

Trail
Top Carriage
Cradle
Recoil cylinder
Springs
Elevating gear
Range gear
Traversing gear
Firing Mechanism
Brakes
Shield
Axle and wheels
Sights
Gravity tank

=The trail= is tubular. The top carriage houses bearings to receive the cradle trunnions and in travel it is locked to the trail. The bronze cradle pivots on the top carriage. The cradle trunnions support the sight.

=The recoil system= is of the hydraulic-spring type. The recoil cylinder is surrounded by the counter-recoil springs which in turn are enclosed by a steel case—all of which is screwed on top of the cradle above the gun. The system operates in the same manner as the 3” materiel with the exception that it possesses the additional feature of a gravity tank which replaces oil lost during firing.

_Recoil Controlling System_
]

_Plan_]

=The elevating mechanism= is of the doubled-ended screw type with the independent angle of site. The gears are so arranged that the elevation for range can be made without disturbing the laying for difference in elevation of the gun and the target, that is, the line of sight. The handwheel on the right is for range to the target while the handwheel on the left is for the angle of site.

=The traversing mechanism= is of the pintle type, consisting of a crosshead, link nut, and an actuating screw with a handwheel. It permits of a 72 mil. traverse either side of the center. A scale strip and a pointer indicate the angle of traverse.

=The firing mechanism= like that of the American 75 is located on the left side of the gun instead of the right side as on the 3” and the French 75. The gun can be fired when it is within 2 inches of the “in battery” position, which increases the possible speed of firing.