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4 Aug 2014 - mkillebrew

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VZ.58 build project
VZ.58 Pictorial

An Illustrative Comparison of the VZ-58 and AK-47

The similarities and interchangable parts are as follows. The 7.62x39 or M43 intermediate round; nothing else is interchangable at the least, and radically conceptually deviant at most. The audience of this is not just the lay person that sees the external resemblance, but those more familiar with firearms in search of an explaination the functionality of each.


To sum up the operating principles of the AK-47 as concisely as possible, it's a automatic firearm whos exhaust gasses are tapped from the barrel moving a gas piston affixed to the bolt carrier rearward, rotating a two-lug bolt that locks to the front trunion in which the barrel is pressed into thereby unlocking the bolt which continues rearward with the carrier, cocking the hammer before it reverses its movement, strips a new round from the magazine and locks back into battery.


In retrospect, the VZ-58 is an automatic firearm whos exhaust gasses are tapped from the barrel which act on a gas piston not attached to the bolt carrier which moves rearward and acts upon the bolt carrier to move it rearward. While the piston returns to its original position recessed inside the gas block, a wedge in the VZ-58's bolt carrier lifts the locking breech block out of the recesses in the receiver. The locking breech block pivots on its rear on the bolt. The bolt itself does not tilt and instead moves directly rearward. In the rearward movement the bolt carrier impacts the disconnector and cocks the striker which operates on a seperate spring from the bolt group spring.

Illustrative Comparison:

I. Locking

Bolt Groups:

VZ-58 bolt group with breech block in locked position. AK-47 bolt group in locked position.

Bolt Groups, continued:

VZ-58 bolt group with breech block in unlocked position. AK-47 bolt group in unlocked position.

Bolt Carriers:

Left: VZ-58 bolt carrier. Right: AK-47 bolt carrier.

Means of unlocking:

Left: VZ-58 wedge inside carrier that lifts breech block. Right: AK-47 recesses that rotate bolt.


Left: VZ-58 bolt with locking breech block. Right: AK-47 bolt; notice two locking lugs.

Breech Block:

Image: VZ-58 breech block, the AK-47 has no comparable component.

Locking Recesses:

Left: VZ-58 locking recesses in receiver rail. Right: AK-47 locking recesses in front trunion.

As evidenced in the pictures, the VZ-58 locks by means of a dropping locking breech block while the AK-47 locks by means of a rotating locking bolt.

II. Gas System

Gas Block:

Left: VZ-58 gas block. Right: AK-47 gas block.

Gas Piston:

Left: VZ-58 gas piston removed, complete with return spring. Right: AK-47 gas piston removed, attached to bolt carrier.

Gas Piston, continued

Left: VZ-58 gas piston in place, top foregrip removed. Right: AK-47 gas piston in place, top foregrip removed.

As illustrated, the gas system on the VZ-58 is a short-stroke as the piston returns to its initial position while the bolt group continues rearward. The AK-47 is a long-stroke as the gas piston is attached to the bolt carrier and therefore must follow the bolt group through its entire cycle.

III. Fire Control Group

Firing Pin Striker:

Left: VZ-58 cylindrical striker. Right: AK-47 hammer.

Striker/Hammer Spring:

Left: VZ-58 Striker spring, attached to receiver cover and positioned directly below bolt spring. Right: AK-47 hammer spring, wraped around hammer crosspin


Left: VZ-58 modified sear to act as semi-auto only with striker cocked. Right: AK-47 sear attached to trigger with hammer cocked.

Sear, continued:

Left: VZ-58 modified sear without striker cocked. Right: AK-47 sear without hammer cocked.

Sear, continued 2:

Left: VZ-58 sear spring, also acts as detent spring for safety and detent spring for top cover retaining pin. Right: AK-47 trigger spring ends rests on trigger/sear assembly acting as a sear spring.


Left: VZ-58 disconnector which disengages the sear from the trigger when struck by bolt carrier. Right: AK-47 disconnector attached to trigger group.

Disconnector, continued:

Left: VZ-58 disconnector spring integral to the trigger group. Right: AK-47 disconnector spring situated below disconnector resting on trigger/sear component.


Left: VZ-58 safety, acts upon trigger arms to clear or engage from sear. safety on. Right: AK-47 safety, acts upon arms of trigger component to restrict movement. safety on.

Safety, continued:

Left: VZ-58 safety disengaged. Right: AK-47 safety disengaged.

Safety, continued:

Left: VZ-58 safety, external. Right: AK-47 safety, external.

> >
The trigger assembly of the VZ-58 deserves more attention to adequately explain its method of operation. The trigger pivots on crosspin driven through the receiver, thereby pulling the trigger arms hinged on its top foreward. A projection on the semi-auto trigger arm acts on the bottom of the sear pulling it foreward, which in turn pulls the rear of the sear where the striker rests down, thereby releasing the striker.

Left: VZ-58 trigger assembly removed. Right: AK-47 trigger assembly removed.

Left: VZ-58 trigger at rest. Right: VZ-58 trigger pulled.

The disconnecting function is also built into this trigger assembly. When the bolt carrier moves rearward it impacts the disconnector arm which is connected directly to the semi-auto trigger arm. This action moves the trigger arm downward to disengage the sear which then returns to its original position under power of the sear spring. This functions in much the same way the safety does, to lower the trigger arm so it cannot engage the sear, but only temporarily.
Image: disconnector protrusion on semi-auto trigger arm.
Unlike other aspects of the VZ-58 and the AK-47, the fire control group cannot be directly compared to eachother because of the radical differences in design. The only similarity they share is that the device is cocked with the rearward movement of the bolt group.

IV. Construction

Construction differers in several key aspects, most notable is the receiver. The VZ-58 is milled from steel and the barrel presses directly into it which is then retained by a barrel pin either pressed in a hole drilled fully through or blind pinned. The AK-47, atleast the AKM of post-1959 manufacture covered here, is stamped 1mm 4130 steel with front and rear trunions riveted in which the barrel presses into. Like the VZ-58, the AK-47 barrel is retained by a pin driven through the front trunion. Headspace on the VZ is determined by how far the barrel is pressed into the receiver in relation to the bolt face, while the AK-47 headspace is determined how far the barrel is pressed into the trunion in relation to the bolt face that locks directly into the trunion. In both the VZ-58 and the AK-47, the fire control groups are retained by crosspins.


Left: Top view of VZ-58 milled receiver. Right: Top view of AK-47 bent receiver.


Left: VZ-58 ejector is a seperate piece pushed into the receiver and retained by detent. Right: AK-47 ejector is integral to the lower rail that the bolt rides on.

Barrel Pin:
Left: VZ-58 barrel pin in lower of receiver. Right: AK-47 barrel pin in upper of front trunion.

Stock attachment:

Left: VZ-58 receiver with threaded hole in rear to accept either side-folding stock or fixed. Right: AK-47 rear trunion with tang that end of stock slides into and through which screws are inserted.

Magazine well:

Left: VZ-58 magazine well milled into receiver. Right: AK-47 magazine well with stamping in receiver to constrict it and hold the magazine tightly

Magazine Latch:

Left: VZ-58 paddle type magazine latch positioned to one side. Right: AK-47 paddle type magazine latch centered.

Receiver Cover:

Left: VZ-58 receiver cover, with bolt and striker springs, retained by push out pin with detent stops in the receiver. Right: AK-47 receiver cover retained by protrusion on protion of the recoil spring assembly that slides into the rear trunion.

Bolt Spring:

VZ-58 bolt spring attached to the top of the receiver cover. Right: AK-47 bolt spring that slides into rear trunion.
Gas Piston Hole:

Left: VZ-58 gas piston hole, notice piston stop at the front to retain piston and spring. Right: AK-47 gas piston hole through upper portion of front trunion.


Left: VZ-58 top handguard retained by detent secured pin at its rear. Right: AK-47 top handguard retained by lever at its rear.

Handguards, continued:

Left: VZ-58 top handguard removed, exposing piston. Right: AK-47 top handguard removed, showing piston tube attached.

Rear Sight:

Left: VZ-58 rear sight secured by lugs that fit into recesses in receiver and held fixed by a leaf spring. Right: AK-47 rear sight secured by lugs that fit into recesses in trunion and held fixed by a leaf spring.

Muzzle Device:
Left: Flash hider on VZ-58 with 14x1 right-hand threading, secured by detent pin. Right: AK-47 traditional slant brake with 14x1 left-handthreading, secured with detent pin.

Bayonet Lug:
Left: VZ-58 bayonet lug, operates indepentant of muzzle. Right: AK-47 bayonet lug, bayonet must lock over muzzle for rigidity.

In contrast to the AK-47, the VZ-58 bolt hold that can be manually actuated, or triggered by an empty magazine. The AK-47 lacks anything comparable.

Image: VZ-58 bolt release situated next to mag release

V. Accouterments


Left: Side view of VZ-58 magazine. Right: Side view of AK-47 magazine.

Magazine, continued:

Left: End view of VZ-58 magazine, notice exposed floorplate on rear edge that engages the bolt holdopen. Right: End view of AK-47 magazine.

Cleaning Rod:
Image: AK-47 cleaning rod secured by lower handguard and gas block. The VZ-58 has no comparable part.

Similarities to other designs

I. VZ-58:

Gas System:
The VZ-58's gas system more closely resembles that of the FN FAL without the ability to adjust bleed as on the FAL.

Left: VZ-58 short stroke gas system. Right: FAL short stroke gas system, less receiver.

Locking System:
The VZ-58's locking system is similar to that of the Walther P-38. The P-38 is not gas operated, but has a hinged block much like the VZ-58, however oriented upside-down. When the P-38 is fired, the recoil moves the barrel rearward until the pin impacts the receiver which pushes on the slope of the locking piece thereby pushing it downward and pulling the locking lugs out of the recesses in the slide allowing it to continue its rearward movement and cycle.

Left: VZ-58 bolt group removed, breech block in locked position. Right: P-38 barrel assembly removed, lug in locked position.

Left: VZ-58 bolt group removed, breech block in unlocked position. Right: P-38 barrel assembly removed, lug in unlocked position.

Left: VZ-58 breech block. Right: P-38 breech block.

II. AK-47

The AK-47 more closely resembles a Desert Eagle than it does a VZ-58 as shown by the following.

Gas System:
The AK-47's gas system is a long-stroke, as with the Desert Eagle. On the Desert Eagle, the piston is attached directly to the slide and recoils fully with it.

Left: AK-47 gas piston attached to bolt carrier. Right: Desert Eagle gas piston attached to slde.

Locking System:
The AK-47's locking system consists of a rotating locking bolt connected to the bolt carrier, while the Desert Eagle's bolt is also rotates to lock inside lugs on the barrel and is attached to the slide.

Left: AK-47 bolt showing locking lugs. Right: Desert Eagle bolt showing locking lugs.

The AK-47's firing system also shares its basic design with the Desert Eagle as its hammer fired instead of striker fired like the VZ-58.

Left: AK-47 hammer cocked inside receiver. Right: Desert Eagle hammer cocked inside frame.