FUSEE SPRING.
On the left of breech casing there is a strong spiral spring called the fusee spring, the rear end of which is connected by the fusee chain and fusee with the crank; the fore-end is attached to the breech casing by means of the fusee spring box and adjusting screw, which passes through the front end of fusee spring box, and through the nut at the front end of spring.
The fusee spring can be adjusted without removing the box, as the vice pin of the screw is loose. This screw is kept in position by two nibs which fall into recesses, by the tension of the fusee spring. The fusee is attached to the crank by means of a stem and lugs, and is easily removed.
To Weigh and Adjust Fusee Spring.
Take out lock; place loop of spring balance over knob of crank handle, and, standing on left side of gun, press down check lever with left hand. Pull spring balance vertically up, resting right wrist on breech casing. The reading indicated when crank handle commences to move will be the weight of fusee spring. This weight should be between 7 and 9 lbs. If spring is over, or not up to weight, adjust by means of vice pin. Generally six clicks (three revolutions) make a difference of about 1 lb. Adjust by ½–lbs. as a rule.
Turning vice pin clockwise increases weight and vice versa.
Tension of spring should always be kept as high as possible, consistent with maintaining normal rate of 500 rounds per minute.