Breech Lock


Figure 97. Unlocking—breech lock being forced out of its recess in the bolt.

The spring is locked in the compressed position by the claws of the accelerator, which engage the shoulders of the barrel extension shank (fig 101).

/. After its initial travel of three-fourths of an inch, the bolt travels an additional 6% inches to the rear, after it is unlocked from the barrel and barrel extension, for a total of 7i/s inches. During this movement, the driving springs are compressed. The rearward movement of the bolt is stopped as the bolt strikes the buffer plate. Part of the recoil energy of the bolt is stored by the driving spring rod assembly, and part is absorbed by the buffer disks in the backplate (fig 102).

24. Extracting a. The empty case, held by the T-slot, has been expanded by the force of the explosion; therefore, it fits snugly in the chamber. If the case is withdrawn from the chamber too rapidly, it may be torn. To prevent this, and to insure slow initial extraction of the case, the top forward edge of the breech lock and the forward edge of the lock recess in the bolt are beveled. As the breech lock is unlocked, the initial movement of the bolt away from the barrel and barrel extension is gradual (fig 97).

6. The slope of the locking faces facilitates locking and unlocking and prevents sticking. The leverage of the accelerator tips on the bolt speeds extraction, after it is started, by kicking the bolt to the rear to extract the empty case from the chamber (fig 98).

25. Ejecting

As the bolt starts its forward movement (counter-recoil) the extractor lug rides below the extractor switch, forcing the extractor assembly farther down, until the round is in the center of the T-slot. The round, still gripped by the extractor, ejects the empty case from the T-slot. The last empty case of an ammunition belt is pushed out by the ejector.

26. Cocking a. When the recoiling groups are fully forward, the top of the cocking lever rests on the rear half of the V-slot in the top plate bracket (fig 103). As the bolt moves to the rear, the top of the cocking lever is forced forward. The lower end pivots to the rear on the cocking lever pin. The rounded nose of the cocking lever, which fits through the slot in the firing pin extension, forces the extension to the rear, compressing the firing pin spring against the sear stop pin (accelerator stop).

b. As the firing pin extension is pressed to the rear, the hooked notch of the extension rides over the sear notch, forcing the sear down. The sear spring forces the sear back up after the hooked notch of the firing pin extension has entered the sear notch. The pressure of the sear and firing pin springs holds the two notches locked together. There is a slight overtravel of the firing pin extension in its movement to the rear, to insure proper engagement with sear (fig 104). As the bolt Btarts forward, the overtravel is taken up and completed when the cocking lever enters the V-slot of the top plate bracket, and is cammed towards the rear; pressure on the cocking lever is relieved as the bolt starts forward (fig 105).

Browning Sear
Figure .98. Unlocking—bolt unlocked from the breech lock.

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  • veikko
    What is the breech pressure browning 50?
    6 months ago
  • lavinia
    Can 50 call machine gun barrel be locked?
    4 months ago

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