M2/M3 BFV: TROUBLESHOOTING - OD1610 - LESSON 2/TASK 1
25mm gun is externally powered and fires from the open-bolt position.
The 25mm gun has a dual-feed capability. It normally has 70 rounds of armor
piercing (AP) and 230 rounds of high explosive (HE) ammo. It can also fire
single shot, 100, or 200 rounds per minute.
Upon trigger signal, a 1.5 hp electric motor drives the bolt and carrier
assembly. The assembly places a live round in the bolt face and removes the
spent case.
If the cartridge has delayed ignition (hangfire) or does not
fire, the weapon will shut down.
In the single-shot mode, the weapon
control card begins shutdown of the system. It releases the sear to catch
the master link. In the low-rate mode, the weapon control card recycles the
system.
In the high-rate mode, the weapon cycles as long as there is a
trigger signal.
Both the feeder and the receiver are connected by a sprocket drive shaft.
The drive shaft drives the chain and feed sprockets at a constant speed in
the same ratio.
(c) 25mm Gun Feed System. Ammo for the 25mm gun is stored below
the weapon in an ammo box.
The box has two sections.
The first section
stores the 70 rounds of AP ammo. The second section stores the 230 rounds
of HP ammo.
Each belt feeds through its own forwarder and chute.
The
forwarders are manually operated. They are used only during the loading of
ammo. For automatic firing of the projectile, the gunner selects the type
of ammo and rate of fire. Also, the gunner chooses ammo and rate for the
ejection of the case and link.
(d) Coax Machinegun. The coax machinegun is gas operated and belt
fed. The feeder cover can be opened or closed without damage to the feeder
cover or ammo.
A trigger signal releases the operating rod and bolt assembly.
The bolt
strips a round from the belt in the feed tray. It stops when the round is
fully in the chamber.
The operating rod forces locking lugs into the
receiver. Then, the firing pin strikes the primer. Burning gases go from
the barrel, through the gas regulator, to the gas piston. The regulator is
at the front end of the operating rod. Gas pressure forces the operating
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