The water jacket was removed and the exposed barrel was redesigned with lengthwise ribbing that not only increased the surface area for cooling but also strengthened the barrel. Despite certain disadvantages, the 1914 Revelli, modified for air use, became the standard defense weapon on Italian aircraft until 1918.
It was apparent that it was necessary to devise some system for collecting the empty cases which were ejected out of the top of the receiver with some force, so a large curved box was devised which performed this function and also accepted the box magazine on the left. This combination tended to make the gun unwieldy but the arrangement was necessary, especially when the gun was fitted to pushers and to the front and rear gun positions of the Capronis.
Function of Revelli’s Wedge Lock
The FIAT Revelli Model 1914 operates on a delayed blowback principal using Revelli’s wedge lock design. On firing, the pressure of the propellant gases, acting through the base of the cartridge imparts a rearward movement to the breechblock (bolt). At this stage the movement of the breechblock relative to the sleeve is controlled by a wedge, which is capable of rotation about a fixed axis at right angles to the axis of the bore. The rearward movement of the breechblock causes the wedge to rotate to the rear. In so doing the wedge, which passes through a slot in the sleeve, bearing against the latter at the shoulder, forces the sleeve, together with the barrel, rearward. After a movement of about 4mm on the part of the moving portions, the wedge is entirely disengaged from the breechblock, which is now free to continue its backward action under its acquired momentum. The wedge is maintained at its lowest position by its nose riding on the under surface of the breechblock. Hence, the sleeve cannot move forward until the recess in the breechblock returns to within about 4mm of its initial position.
The axis of the wedge is eccentric, and can be adjusted in one of three fixed positions in its bearings. This enables the amount of jamming effect of the wedge on the moving parts to be increased or decreased to ensure the smooth working of the gun.
The return of the moving parts to the firing position is caused by a strong spring operating through a connecting rod, one end of which is hooked to a claw on the bottom of the wedge, the other end being connected to an adjustable spring, which, in its turn, is attached to the frame of the gun.
The claw does not assist in the locking of the action, but is the medium by which automatic firing is controlled.
The FIAT Revelli Model 1914 uses a unique box magazine sometimes referred to as a “mousetrap action” or a “squirrel cage.” The gun primarily used a box magazine containing 50 rounds though a 100-round box magazine was employed for anti-aircraft use. Both box magazines are identical except for the number of cartridges used. The 50-round box magazine is small and compact and can be quickly inserted into the left side of the gun.
The 50-round box magazine is actually ten separate 5-round magazines contained within one box. The magazine may be loaded in one of two ways: individually loading a round in a single column at a time, or by groups of five across the top using a special wood magazine loading tool.
To load one column at a time, a small metal protrusion attached to the magazine follower in each column section is depressed with the thumb of the left hand, which is also holding the magazine box. The base of the cartridge is inserted and forced down under the cartridge retaining lips with the right hand. They are then slid back to be seated against the rear of the box. Five cartridges are then fed into each of the magazine columns one at a time.
To load the magazine using the wood loading tool, five cartridges are placed on top of five magazine followers to the front of the cartridge retaining lips. Using the five section wood loading tool, align and place the loading tool on top of the five cartridges. Press down to the rear and slide the five cartridges under the cartridge retaining lips and seat to the rear.
The loaded magazine is inserted in guides in the feedway on the left-hand side of the gun. As each cartridge in the column is chambered, the compartment spring forces the next cartridge upward, ready to be chambered by the forward movement of the bolt. When the fifth and last cartridge in the compartment has been fired, the small metal protrusion attached to the follower in the rear automatically engages a trip lever pawl that indexes the magazine one column to the right; where the feeding process is repeated. When all ten magazine columns have been indexed to the right and the magazine is empty, it is ejected from the feedway on the right side of the gun. The magazine indexing pawl may be disengaged to allow removal of a partially expended magazine. The indexing pawl disengaging lever is located on the bottom of the receiver directly behind the feedway.
Turn the fire control selector switch, located at the rear of the gun just above the thumb trigger, straight up into the vertical position to the “Secura” (safe) setting.
Insert a loaded magazine into the guides in the feedway on the left hand side of the gun and push to the right until the feed indexing pawl engages the box magazine.
Open the hinged ejection port cover located on the top of the receiver directly above the feedway. (Empty cartridges are ejected out through the top of the gun and deflect to the right.)
With the fingers of the right hand, grasp the cross arms of the cocking handle and pull straight to the rear. This compresses the main spring. Release the cocking handle and the breechblock (bolt) will travel forward, strip a cartridge from the box magazine and chamber it while connecting the firing mechanism.
Turn the fire control selector switch to the left (Lento) for single shot or to the right (Rapido) for full automatic.
Grasp the two spade grip traversing handles with each hand and press the thumb trigger forward to fire the gun.
Field Stripping the FIAT Revelli Model 1914
A large pin at the rear of the receiver locks the spade grip traversing handles and trigger mechanism to the receiver. Pull the pin out to the left and drop the handles down to a horizontal position.
Pull out and back on the spring held knob on the right hand side of the gun directly below the cocking handle. Slide the inspection plate in the guide to the rear and out of the gun. This exposes all the internal operating mechanisms, except for the breechblock (bolt), for inspection and adjustment.
Press the spring release catch on the receiver lock pin, located just below the rear sight base and which passes through the gun. Pull out and remove from the right hand side.
The cocking handle and breechblock, complete with recoil spring and firing pin, may now be drawn to the rear and out of the gun.
Unscrew the firing pin from the breechblock and separate.
This completes the basic field stripping of the weapon. Reassembly is in the reverse order.