In full automatic action, the side plate is pushed back to point "R". In this position the pin inside is turned so that its cam faces the trigger lever, thereby advancing the trigger lever about .25 inch to the front. This changes the angle of trigger nose to sear lever; hence when the trigger is pulled, while the sear lever is elevated somewhat it still cannot slip off the nose of the trigger lever. Thus as long as finger pressure is maintained, the sear cannot engage with the hammer bent to hold the hammer back, and the arm will continue to fire as long as there are cartridges in the magazine.
While in some Spanish imitations of his pistol, the hammer follows the breechblock down to fire, this is not a good sear design. In the genuine Mauser a secondary sear is provided to make sure that the arm is completely locked before the firing of each round.
This secondary sear automatically holds the hammer back until the breechblock is fully locked, at which time it automatically releases.
It is positioned below and to the rear of the hammer pivot nearly opposite the primary sear. Like the primary sear, it has a broad bearing surface, reaching the entire width of the tumbler.
The secondary sear is a single unit having a wide bearing in each wall of the receiver. Its right side is shaped as a flat lever having unequal arms which position in recesses in the receiver, and it is flush with the primary sear spring and its lever. The lower arm is the shorter one. It engages with the disconnector bar. The long upper arm curves to the front where it ends in a rounded open hook projecting above the receiver into a slot in the underside of the barrel extension. This arm can move only within the limit provided by its recess. It is operated by a small coil spring and plunger mounted in a tunnel in the side of the receiver below the primary sear spring.
When the sear is in its notch, this upper arm projects above the level of the lock frame or receiver, and a forward movement will bring it below this lever. Thus as the breechblock travels to the rear and rolls over the hammer, the main bent is first caught by the primary sear and then by the secondary sear in its bent. As the secondary bent is cut further in the tumbler than the primary one, when the arm is firing full automatic, the hammer fall is somewhat longer as it is released by automatic or secondary sear action.
When the plate is set for full automatic fire, pressure on the trigger results in the primary sear being kept out of its bent as the hammer falls. As the breechblock during rearward movement unlocks from the receiver when the barrel is halted, the hammer tumbler after passing over the primary sear engages the secondary (automatic) sear momentarily.
Since the barrel extension is in full recoil at this point, the upper arm of the secondary sear thrust by its spring, rises up into its cut in the underside of the extension. The bent cannot engage until this point is reached.
The compressed recoil spring now reasserts itself and drives the breechblock forward to strip the top cartridge from the magazine and drive it toward the chamber. During the closing movement, the barrel extension begins this forward movement as the mainspring acts upon it through the rocker and the bolt lock. Thus the rear end of the slot in the underside of the barrel extension pushes the upper arm of the automatic or secondary sear, thereby releasing it from its bent, and permits the hammer to continue forward to hit the firing pin and fire the cartridge when the breech is fully locked.
The automatic disconnector during full automatic fire is unusual. There is a bar which can move in a groove in the bottom of the receiver. Its front connects with the transverse pin of the fire control lever, and its rear engages with the short bottom arm of the sear» When this bar is to the rear during normal fire, the secondary sear is held out of its bent and also out of its engagement with the barrel extension by this action.
The safety pivot pierces the side of the receiver. A recess in the side of the hammer which receives this pivot to serve as a safety bar is cut out so that when the "safe" position is reached, the hammer can still be released by trigger pressure but will be halted in forward motion before it can hit the head of the firing pin.
On this design of universal safety, the sear is carried further to the rear on the left into a recess in the safety lever. The lever is cut to permit movement of the sear only at the fire and at the safe positions. It cannot function at any intermediate point. Thus when the hammer is up and the safety is applied, pulling the trigger cannot accidentally fire a cartridge, for as the hammer falls its fall is positively halted before hitting the firing pin.
Like all earlier Mauser military pistols, this arm is designed to be used with a stock shoulder holster. However it should be noted that the grip is larger and thicker than that of the standard Military Model pistol and the two stocks will not interchange.
While in theory this is an efficient police pistol, in actual practice the cartridges are discharged so rapidly and the muzzle elevates so quickly that it is not an efficient full automatic design. The full automatic feature is of value only in very unusual cases of emergency.
Following are the characteristics of this model 712:
The caliber is 30 (7.63mm Mauser). It uses the standard 7.63mm Mauser cartridge as already described.
The overall length of the pistol is 11.3 inches. The length of the barrel complete with its chamber is 5.2 inches. (It must be remembered in this design that the barrel extension which houses the breechblock is an integral part of the barrel forging, extending back from the chamber and being suitably cut away to permit recoil travel and also to house the breechblock assembly).
The weight of the arm is 2.79 pounds without the stock and with the 10-shot magazine inserted but empty. With the 20-shot magazine (empty) inserted it weighs 2.9 pounds.
The arm may be loaded from Mauser clips from above or by insertion of box magazine from below as already outlined.
While the rear sight is graduated to only 1000 meters, the cartridge in this pistol has an extreme range of about 2200 yards.
The muzzle velocity with standard barrel is about 1392 feet per second and the muzzle striking energy about 366 foot pounds.
At 50 meters the penetration is 8 to 9 inches in soft pine.
This weapon may be immediately identified by the Mauser trade mark on the left side of the receiver to the rear of the sliding fire control plate. It is manufactured of the finest materials to the finest standards of workmanship. It should not be confused with arms which look very much like it which were made in Spain; those are differently constructed mechanically and are neither as strong nor as reliable. The original Mauser Model 712 was first generally marketed in 1931.
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