SECTION B

MACHINE GUNS

MARLIN AIRCRAFT MACHINE GUN




DESCRIPTION

The Marlin aircraft machine gun is designed for fixed mounting and for use with a synchronizing device, either mechanical or hydraulic. It is fed from a disintegrating metallic link belt made up in 500-round lengths or more. The weight of the gun is 22 pounds, and the rate of fire, 680 shots per minute. The gun is described in detail in Ordnance Pamphlet No. 1933.

Marlin guns are packed for shipment in a wooden box 6 by 46 inches by 8-1 inches deep, each box containing one gun and its spare parts.


POINTS TO BE OBSERVED BEFORE A FLIGHT

The gun should have been thoroughly inspected for defective or worn parts, and all such parts replaced with new ones.

Test the operation of the "trip" by pulling the charging slide to the second notch and letting it slam down on the gauge.

Test the operation of the "no trip" by pulling the charging handle all the way to the rear and letting it slam-down on the gauge.

All parts of the gun must be clean; special attention should be paid to the gas piston and gas cylinder, since these parts are directly subjct to the action of the gases and are therefore very liable to rust.

The following parts require particular attention in oiling:


See that the gas adjuster thimble is screwed in tight.

Work the mechanism slowly back and forth several times ~y means of the charging slide to see that there is no excessive friction. If the mechanism does not work freely, the cause of the trouble must be found and remedied. Put several dummy cartridges through the gun to see that it is functioning properly.

Inspect the loaded belt for correct alignment of cartridges. See that gun is firmly fixed on its mount.

Make sure that the synchronizer will trip the trigger when the propeller is in the proper position.

Inspect the loaded belt for correct alignment of cartridges. See that gun is firmly fixed on its mount.

Make sure that the synchronizer will trip the trigger when the propeller is in the proper position.


MARLIN AIRCRAFT MACHINE GUN, FIRING MECHANISM

Figure 2B shows the lock container of Model 1917 Marlin aircraft machine gun. This firing mechanism is not so satisfactory for synchronizing, in that if the trigger is released before the mechanism has reached the tripping position, the gun will fire when the sear is released by the trip, provided that the ressure of the trigger motor piston has not been removed from the trigger.

This slight delay in operation means that when the gun does fire it will be out of synchronism with the propeller.

Figure 3 shows the arrangement of parts in the lock container of the Model 1.918 Marlin aircraft machine gun.


Another trigger has been added which floats on the trigger and sear pin and fits in the same notch on the hammer with the sear. The rear end is backed up by a spring which tends to keep the hook on the front end pushed forward out of contact with the lug (a) on the synchronizer trigger.

The synchronizer trigger has been redesigned so that the piston acts on its cam surface within the lock container, and a small lug has been added to the right-hand side which may be engaged by the hook of the trigger.

The hammer has been lightened by cutting in the shape shown,, and its stroke has been reduced to about three eighths inch.


OPERATION

In ordinary operation when the sear is released the hammer drops onto the. trigger, causing the trigger to move to the rear, compressing its spring and causing the hook to engage with the lug on the synchronizer trigger.


When the piston now strikes the cam on the syncronizer trigger, the synchronizer trigger is forced up and lifts the
trigger out of engagement with the hammer. The hammer is then free to fall and strike the firing pin.

In case the synchronizer trigger has been struck by the synchronizer piston before the sear has been released by the trip, the syncronizer trigger alone is raised and does not lift the trigger with it, since the trigger is held forward by the trigger spring so that its hook is not engaged over the lug on the synchronizer trigger. Now the lug on the synchronizer trigger is directly behind the flat end of the hook on the trigger, and when the sear is tripped the hammer falls onto the trigger, forcing it to the rear so that the flat end of the hook bears against the lug on the synchronizer trigger. The hammer is thereby prevented from falling.

As soon as the pressure of the piston is released from the synchronizer trigger, the synchronizer trigger is forced down by the synchronizer trigger spring, allowing the hammer to force the trigger to the rear so that it hooks over the lug on the synchronizer trigger. We now have the condition already explained in the preceding paragraph (sketch A) and the gun is fired at the next impulse of the synchronizer piston.


TRIGGER MOTOR

The, Model 1918 Marlin guns are supplied with a trigger motor attached to the lock container, adapted for connection to a C. C. synchronizing gear. The trigger motor consists of a piston and spring contained in a bronze cylinder which is screwed into the forward end of the lock container.




The cylinder is provided with a coupling nut and tube end into which the main pipe line may be soldered. A small vent screw located on top of the cylinder allows for the release of air from the system.

The C. C. synchronizing gear trigger motor as used with the Model 1917 Marlin aircraft gun is shown in figure (29), page 57.


ELECTRIC HEATER FOR MARLIN AIRCRAFT MACHINE GUN

In order to prevent the oil gumming due to low temperatures when flying at high altitudes, electric heaters have been devised for the Marlin aircraft machine gun.


This electric heater consists of a resistance grid surrounded by insulating material and is riveted to inside of the bottom plate of the gun. It is connected with a bayonet plug on the underside of the bottom late which provides for connection with the leads. The heater consumes 60 watts at 12 volts and is fed from the generator which supplies the lighting and heating system.



SPARES FOR MARLIN GUN

The following spare parts are supplied with each Marlin aircraft machine gun and are packed with the gun in the packing case:

2 action springs.
I barrel.
I bolt complete.
4 bolt pins.
4 buffer springs.
2 carrier dog springs.
I carrier dog plunger spring guide.
2 carrier stop springs.
3 cartrid-,e extractors.
2 cartridge extractor cam aprings.
3 cartridge extractor cams.
3 cartridge extractor pins.
I cartridge guide, left-hand.
I cartridge guide, right-hand.
2 cartridge retainer plunger springs.
2 charging slide tension springs.
2 ejector springs.
2 feed throw-off springs.
5 feed wheel dog pin cotter pins.
2 feed wheel dog springs.
2 feed wheel dog pin washers.
2 firing pins.
4 firing pin springs.
2 firing pin stop pins.
I hammer.
2 hammer springs.
I hammer spring guide.
I piston rod lock pin.
I piston rod lock pin spring.
5 ratchet lever pin cotter pins.


BASE SPARES

4 ratchet lever pawl springs.
2 ratchet lever pin washers.
1 sear.
2 sear springs.
8 shell extractors.
8 shell extractor pins.
8 shell extractor springs.
1 trigger.
4 trigger springs.
1 trigger and sear pin.
Needles.
Needle screws.
1 canvas protecting cover (for barrels).
1 combination gas adjuster, wrench and screw driver.
1 combination barrel wrench, screw driver and action spring tool.
1 defective cartridge extractor.
4 drifts (1 set).
1 oil can.
1 solid cleaning rod.
1 trip gauge.
1 rear mounting bracket (fitted to gun when shipped).
4 rear mounting bracket screws (fitted to gun when shipped).
1 paper container for spares.
1 belt loading machine and box for every four guns.

With every overseas shipment of 1,000 or more aircraft machine guns, the necessary amount of base, spares for the guns are also shipped. Base spares consist of parts of the guns in sufficient quantities calculated to best meet the demands of service.