Chapter XIV: Part VI: Recoil

1. What is meant by the _recoil_ of a piece of artillery?

The retrograde motion impressed upon cannon by the discharge is termed the _recoil_.

2. What causes the recoil of a piece?

The gas produced by the ignition of the charge in the bore, expanding with equal force in every direction, finds only two ways of escape (the muzzle and vent); the pressure upon these points will therefore cease, while it will be proportionally increased upon the parts directly opposite, that is, the breech and the lower part of the first reinforce, producing in the first case the recoil, and in the other, indirectly, the dipping of the muzzle.

3. How far does a gun usually recoil?

This depends entirely upon the nature and inclination of the ground upon which the carriage stands, the situation of the trunnions, angle of elevation, comparative weight of the gun and carriage, and upon the strength of the charge.

4. What proportion does the velocity of the recoil of a piece bear to that of a ball?

The proportion is inversely as their weights, or their masses.

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5. What proportion exists between the pressure acting upon the part of the bore of a piece directly opposite the vent, and that which occasions the recoil?

As the square of the diameter of the vent is to the square of that of the shot.

6. Has the recoil any effect upon the flight of the projectile?

No appreciable effect, the shot being expelled from the gun before it has recoiled a fraction of an inch.

7. What are the principal inconveniences arising from the recoil of guns?

The necessity of running up the gun after every discharge, and consequent fatigue to the men and loss of time; it also necessitates that a greater breadth should be given to the terreplein of a work.

8. What causes the muzzle of a piece of artillery to dip when fired?

The sudden pressure of the gas acting upon the portion of the first reinforce opposite to the vent, causes the piece to strike downwards upon the elevating screw or quoin, and the reaction to make the muzzle dip.

9. What influence has the position of the axis of the trunnions in respect to that of the bore upon the recoil?

If the axis of the trunnions be below that of the piece, the pressure of the breech upon the carriage will increase as the distance between the axes increases; and from this pressure there will arise a friction upon the ground which will diminish the recoil. On the contrary, if the axis of the trunnions, be above that of the piece, the breech will have an upward tendency, the recoil will be increased, but the carriage, and particularly the axle-tree, will be subjected to less strain. Hence, the recoil will be transmitted directly to the trunnions, if their axis (as in our service) be situated in the same plane with the axis of the piece. The size of the trunnions is made proportional to the force of the recoil.

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10. Does the position of the trunnions with reference to the centre of gravity of the piece influence the recoil?

Yes; in cannon fired horizontally, or under very small angles, the portion in rear of the trunnions is heavier than that in front; an arrangement which increases the pressure of the trail on the ground so as to diminish the recoil. But in pieces fired under large angles, the trunnions are placed in rear of the center of gravity, for the purpose of increasing the ease of pointing.

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