Heckler&Koch VP9 - Manual (Page 6)

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SECTION 4 FUNCTION AND OPERATION
CYCLE OF OPERATION
The cycle of operation is a reoccurring sequence of mechanical events which takes place
in the operation of a self-loading firearm. The sequence for the VP9 begins with a loaded
magazine inserted into the magazine well with the slide locked back to the rear.
1. Feeding: Removal of a round from the magazine
Depressing either side of the ambidextrous slide release or pulling slightly back on the
charging supports allows the recoil spring to expand, driving the slide forward. The feed
pawl, an extrusion that is located on the bottom of the slide, passes between the feed
lips of the magazine tube, striking the top round and pushing it towards the chamber.
The projectile then contacts the barrel’s feed ramp, allowing the base of the cartridge to
pivot upwards on the slide’s breech face.
2. Chambering: Placing and seating the round into the chamber of the barrel
The recoil spring continues to expand, driving the slide forward and the slide positions
the cartridge into the chamber. The base of the cartridge continues to pivot upwards
as the slide mounted extractor engages the cartridge’s extractor rim. Chambering is
complete by the time the barrel starts to move when the slide comes in contact with the
back of the barrel’s locking block and starts to pivot the barrel upwards and forward.
3. Locking: Closing and locking of the breech mechanism prior to the shot
As the slide is moving forward, the slide’s breech face contacts the extension on the back
of the barrel’s locking block and thus pivots the barrel upward until the stepped forward
edge of the barrel locking block engages the forward edge of ejection port. As the slide
locks into position, the frame mounted disconnector is allowed to pivot upwards into a
corresponding relief cut milled on the inside of the slide, thus allowing the trigger bar
access to sear release catch. The locking phase is complete when the slide reaches its
limit of forward travel.
4. Firing: Ignition of the cartridge’s primer and propellant
As the operator pulls back on the trigger, the trigger safety latch pivots upwards, thus
allowing the trigger to be pulled back towards the rear. The trigger bar, connected to the
trigger moves back as well, allowing an engagement surface on the trigger bar to pivot
the spring loaded firing pin safety to the side which allows the firing pin to move forward
once the trigger is pulled. The trigger bar continues to move to the rear until the back of
the trigger bar contacts and then presses downward on the sear release catch. The sear
release catch, in turn, pushes downward on the catch, disengaging the catch from the
firing pin and then allowing the firing pin to move forward, being driven by the expansion
of the firing pin spring. The tip of the firing pin contacts and then pierces the primer. The
primer detonates which, in turn, ignites the propellant. The projectile, separated from the
cartridge case, is forced down the barrel by the expanding gases and is stabilized by the
polygonal rifling located inside the bore.
5. Unlocking: Removal of any blocking mechanism to allow the opening of the breech
The resultant force of the cartridge firing produces an impact on the slide and barrel,
initially pushing both the slide and barrel back in unison. The slide’s ejection port pushes
back on the barrel locking block and after approximately 4.5 millimeters of travel, pivots
the barrel downward until the barrel’s angular locking surface engages the contact surface
on the frame mounted locking block.
6. Extracting: Removal of the fired cartridge case or live round from the chamber
With the barrel now retained by the locking block, the slide continues to move towards
the rear. The extractor pulls the fired cartridge case or live round from the chamber.
7. Ejecting: Expulsion of the fired cartridge case or live round from the firearm
The extractor engages the cartridge case’s extractor rim as the barrel travels to the rear.
The extractor creates a pivot and the frame mounted ejector creates a contact point, as
the slide rakes the cartridge case against the ejector, allowing the ejector to expel the
cartridge case out through the ejection port.
8. Cocking: Resetting of the trigger mechanism to allow subsequent shots to be fired
In the first few millimeters of rearward travel, the slide passes over the disconnector and
presses it downward, thus precluding the trigger bar from depressing the sear release
catch and immobilizing the firing pin system. As the slide continues to move back towards
the rear, the frame mounted catch engages and pushes back on the lug mounted under-
neath the firing pin, thus compressing the firing pin spring and cocking the firing pin.
SAFETY FEATURES — The VP9 incorporates the following safety features:
1. Firing Pin Safety
The slide mounted firing pin safety helps prevent accidental discharge from impact if
the VP9 is struck or dropped. When at rest, the back of the spring loaded safety pivots
towards the center of the slide and engages a tang that extends downward on the
bottom of the firing pin and thus blocks the firing pin from moving forward in the firing
pin tunnel. Once the trigger is pulled, an engagement surface on the trigger bar pivots
the firing pin safety to the side and allows the forward movement of the firing pin.
2. Trigger Safety
The frame mounted trigger safety also helps prevent accidental discharge if the VP9 is
struck or dropped by blocking the rearward movement of the trigger assembly thereby
immobilizing the trigger bar, unless the entire trigger is pulled back to the rear. With the
trigger bar unable to press downward on the sear release catch, the catch remains upright
and holds the cocked firing pin assembly in place.
3. Disconnector
The frame mounted disconnector ensures that the VP9’s slide must be in battery before
allowing the trigger bar access to disengage the sear release catch and thus preclude the
release of the firing pin. When out of battery, the disconnector is pushed downward by
the slide. In battery, a relief cut milled on the bottom of the slide allows the disconnector
to pivot upwards and allows the trigger bar to travel rewards to disengage the sear
release catch.
4. Disassembly Safety
The disassembly safety ensures that the magazine must be removed from the magazine
well, the chamber be cleared, and the firing pin decocked prior to disassembly. The
dismounting safety is pivoted upwards by the presence of a magazine (loaded or
unloaded) and thus blocks the operation of the disassembly lever. When the magazine is
removed, the dismounting safety pivots downward and allows the disassembly lever to be
rotated forward.
The bottom of the barrel locking block prohibits the operation of the disassembly lever
when the slide is forward. Having to lock the slide to the rear prior to manipulating the
disassembly lever ensues that any round present in the chamber is extracted and ejected.
The activation of the disassembly lever also decocks the firing pin by repositioning the
trigger bar slightly forward. The slide then presses downward on the trigger bar which
disengages the catch from the firing pin.
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