This is the next report on Jordan Thompson’s VZ 35. We know him as Starboard Rower. Be sure to read parts 1 and 2.

He talked to me about his VZ 35 at the Arkansas airgun show and I asked him to write this guest blog about it. This is an air rifle we seldom hear about!

If you’d like to write a guest post for this blog, please email me at blogger@pyramydair.com.

Take it away, Starboard Rower.

VZ 35 training rifle: Part 3

Vz 35 rifle with bayonet
The VZ 35 with bayonet.

by Jordan Thompson

History of airguns

Part 1
Part 2

This report covers:

  • Basic operation
  • Ammunition type
  • Caliber
  • Technical Requirements Evolve During 1935 Development
  • Personal experience
  • Velocity test #1
  • Oil the Piston Seal
  • Velocity test #2
  • Velocity test #3|
  • Final thoughts

In parts 1 and 2, we dug into the VZ 35′ s history. Today, we will begin taking a look at its performance. Let’s start with a discussion about ammunition and caliber. Then we’ll investigate the velocity of this particular specimen.

Basic operation

Recall that this rifle was the result of a military contract.  The Czechoslovakian army needed a training rifle that would closely emulate the handling of its firearm cousin, the VZ 24.

The call for design proposals in 1934 prescribed ten different technical requirements for the air rifle’s design.  This included bolt operation, safety operation, trigger pull weight, rifle weight, sight distances, and 4.45 mm round shot.

VZ 35 Factory
The Czech factory where the VZ 35 was made.

Ammunition type

Today, we would say that this air rifle uses round lead balls. These are not the same as BBs, though both are spherical and that leads to some confusion in terminology. Modern BB’s are typically steel and 4.4 mm (.173-inches) in diameter.

A spherical shape offers some advantages to a repeating airgun, in that it allows for more reliable feeding.  In this case, the VZ 35 has a gravity-fed hopper. The round ball simply has to drop into position with each operation of the bolt. Orientation does not matter, as it would for a diabolo-shaped pellet.

Caliber

The VZ 35 is most often referred to as using 4.45 mm ammunition. We see 4.45 mm in the original 1934 Vojensky Technicky Letecky Ustav(VTLU) call for proposals referenced above. VTLU is the Military Technical and Aviation Institute. We also see 4.45 mm referenced in many secondary sources of information today. These include websites, blogs, and the rare publication.

I believe it is more accurate to say the VZ 35 uses 4.40mm ammunition.  I’ll offer a few reasons.

Technical requirements evolve during 1935 development

First, technical requirements evolved during the airgun’s development.  The original 1934 call for 4.45 mm rounds was almost certainly with an eye towards Sellier & Bellot’s No. 10 round ball ammunition, readily available at the time.

Field trials of the VZ 35 were conducted in Milovice during the Spring of 1935. Milovice had a large infantry school and proving ground. It was the Czechoslovak equivalent to Aberdeen, Maryland in the U.S. Sellier & Bellot initially provided 60,000 4.45 mm rounds for testing.  Performance of the early pre-production airgun with this ammo was disappointing.

VZ 35 Air rifle training
The Czech army wanted an air rifle with which to train.

Experiments were then conducted with different bore diameters of 4.39, 4.41, 4.44, 4.46, and 4.48 mm. They also tried smooth and rifled bores. Ultimately, a rifled bore with 12 grooves was selected.

Many more refinements were conducted in close collaboration between Frantisek Myska (designer from the Strakonice factory, and Captain Zeman Františka (representative of VTLU). These refinements were focused on improvements to accuracy, reliability, and durability. The VTLU required an endurance test of 50,000 rounds. To put that in context, it’s closest competitor in 1935, the Haenel Model 33, was rated for 17,000 rounds.

In the end, even the ammunition itself was modified.  They settled on a metallurgical composition of lead alloyed with 2.5% antimony.  Unfortunately, it is not clear from contemporary sources what the final ammunition/bore diameter was.   However, it is accepted today that the VZ 35 uses a smaller caliber than the later VZ 47, which was 4.46 mm.

Find a Hawke Scope

Personal experience

In my VZ 35 a 4.40 mm round simply fits better. I sourced it from JG Airguns. You can find other ammo advertised as being compatible for the VZ 35/Haenel 33 and similar inter-war airguns. But trying them, I can feel resistance when the bolt probe pushes the round into the barrel. It can get stuck in the barrel during firing. Or worse, can leave fine shavings of the ammo coating behind in the hopper.

VZ 35 Bolt probe
The bolt probe at the bottom of the hopper shoves the ball into the rifled barrel.

Ammo that I have tried unsuccessfully include:

The copper-jacketed H&N Pazisions-Rundkugel 4.45 mm lead round ball.

VZ 35 H&N ammo
H&N 4.45 mm Precision round balls didn’t work in my VZ 35.

New-old-stock VZ 47 Czechoslovak army surplus ammunition. This ammo is sealed in a Sellier & Bellot tape, and labeled as 4.45 mm.

VZ 47 ammo
VZ 47 ammo, which is 4.45 mm, also failed to work in my VZ 35.

Clearing a stuck round was a good opportunity to clean the bore.  After six or seven patches, some JB Non-Embedding Bore Cleaning Compound, and a final bit of Ballistol, I knew it was clean.  The bore felt smooth and consistent.

VZ 35 Cleaning bore
After cleaning the bore with JB Bore Paste and Ballistol, the bore felt smoother.

If my VZ 35 is typical, I’m calling it a 4.40 mm caliber airgun. Notably, The Blue Book of Airguns agrees — 4.40 mm.

Velocity test #1

When I first purchased the gun, I shot an initial test right out of the box.

I used the JG Airguns 4.40 lead round ball.  These average 7.1 grains.  Thirty shots total.  I won’t bother showing the shot string. The average velocity was 368 f.p.s. with an extreme spread of 184 f.p.s.

VZ 35 4.40 mm round balls
I got these 4.40 mm round lead balls from JG Airguns.

VZ 35 Rifle with chronograph
The chronograph told a sad story.

Ouch! This airgun works. But that extreme spread is far too wide.

What should we make of the velocity? Well, let’s compare it to the original 1935 trials at Milovice. The VTLU called for a speed of 135 to 140 m/sec, where the spring had to endure the first 25,000 shots without the speed dropping below 125 meters per second. By comparison the Haenel 33 velocity was documented as 80 meters per second. That’s considerably slower.

Using the lowest target value of 125 meters per second, that equates to 410 f.p.s.  So, my gun is shooting below spec.

Oil the Piston Seal

I suspected the leather seal on this gun was bone-dry. Externally, it appears well cared for. But it may have been decades since it was last fired. Who knows? I love the mystery of these old guns.

I oiled the seal with SAE 30W non-detergent oil, using a needle oiler. After quite a few drops I leaned the gun up against a wall, muzzle down, to soak overnight.

VZ 35 Oil
I oiled the leather piston seal with 30-weight non-detergent oil.

Velocity test #2

We’ll use the same JG Airguns 4.40 lead round ball at 7.1 grains.  Thirty shots, again. The average this time was 423 f.p.s. with an extreme spread of 73 f.p.s.

This is better. The rifle has reacted well to oiling. I now suspect the leather seal is largely intact, or at least present in some form. After 86 years that is all I could hope for.

Velocity test #3

Three months later I tried again. Would the leather seal be better conditioned?  Once more, I oiled the piston seal, overnight. Same ammo; same thirty shots. This time the average was 419 f.p.s  with an extreme spread of 51 f.p.s.

We are not seeing significant improvement.  I believe the oil has done its job and we will now move on to other things.

Final thoughts

The extreme spread is still just too much. The hopper seal is visibly degraded. It is now suspect number one. Before moving on to accuracy tests, I’d like to get it cleaned up and a fresh seal in place.

I am evaluating cutting my own leather ring, or perhaps sourcing a rubber one.  We have seen examples of both in photos of other VZ 35s.  Interestingly, rubber appears to be original.

I will also need to take care in removing that old gunk, which was probably a prior owner’s attempt at a repair.  I wouldn’t be able to sleep if I marred the beautiful finish!