Saturday, 5 September 2020

A Bullpup for Occupants

In addition to German-made anti-tank rifles, the Wehrmacht and its allies used foreign anti-tank rifles in WWII. Some of them were captured, and some were built to German orders. The latter largely applies to Czechoslovakian designs, which were of interest to the Germans even before the annexation. The Czechs were working in two directions at once.

Pre-war experiments

The Czechoslovakian army announced a tender for an anti-tank rifle in 1935. One of the bidders was František Janeček, best known as the designer of JAWA motorcycles, but then specializing in squeezebore anti-tank rifles that used the Gerlich principle. Interestingly enough, the principle was realized via a special adapter. Removing it allowed the anti-tank rifle to fire regular 15 mm ammunition from the ZB-60 heavy machine gun.

Janeček's experimental 15/11 mm squeezebore anti-tank rifle.

The first 15/11 mm rifle was too heavy, up to 20 kg, and in November of 1936 the military clarified that the rifle needs to be smaller and usable by one person. Orders were given in February of 1938 to focus on the 7.92 mm caliber. The military expected any rifle using the 15 mm cartridge to be too heavy.

Nevertheless, design of squeezebore rifles continued even after annexation. 15/11, 11/7.92, 7.92/5.6, and 9/7 mm rifles were developed. None of these rifles made it out of the prototype stage. "Classical" rifles did better, but even then their success was limited.

These rifles were designed in part by Josef Koucký, a talented Czech arms designer who will later develop the famous CZ-75 pistol jointly with his brother František Koucký. Like his colleagues, Koucký expected success to lie in speeding up the bullet. He didn't delve into squeezebore guns, but jury's out on whether or not his solution was better.

The caliber he used was the standard 7.92 mm, one of the most common calibers in Czechoslovakia after WWI. The young republic acquired tooling from Mauser as reparations, and so most post-war Mauser rifles were actually built in Czechoslovakia. A very long casing was needed to give this bullet a high velocity. The 7.92 mm ZVV (7.92x145) achieved speeds of up to 1270-1320 m/s according to some sources.

Bullets used in the conical 15/11 mm anti-tank rifle before and after being fired, as well as the core.

Of course, a long barrel was needed to allow the bullet to reach its full speed. Striving to keep the length of the rifle within reasonable limits, Koucký designed a bullpup rifle. The ZK 382 had a chance to enter history as not only the anti-tank rifle with the longest round, but also one of the first mass produced bullpup rifles.

There is no precise information about the penetration of the ZK 382, but one can assume it could easily punch through interbellum light tanks with bulletproof armour. However, either news about tanks with shell-proof armour reached Brno or Koucký decided to make his gun futureproof, but his followup designs were created for even a more monstrous cartridge.

ZK 382 rifle.

The ZK 384, 385, and 395 were supposed to use the 12x165 mm cartridge. One of them, the ZK 384,  the variant fed by either 5 or 10 round magazines weighing over 15 kg, is on display at the military museum in Prague. The ZK 385 was single shot, the ZK 395 was magazine fed again, but only 5 round magazines were used. With a claimed muzzle velocity of 1300 m/s these bullets would be dangerous even to first generation tanks with shell-proof armour.

Orders of the Black Order

Allied tankers should thank the occupying Germans for paying little attention to Koucký's works. The Werhmacht also considered the 7.92 mm caliber to be sufficient for an anti-tank rifle, and the Germans settled on a round with a mere 94 mm long casing. This rifle was much weaker than the Czech monster. The next Czech anti-tank rifle was made for this round. This was a bullpup with a 5 round magazine. It was accepted into service with the SS as the Pz.B. M.SS 41.

The Pz.B. M.SS 41 anti-tank rifle.

After war broke out with the USSR, the rifle unsurprisingly ended up on the list of Soviet trophies. It was carefully studied by Soviet specialists. Preliminary inspection at the Main Artillery Directorate (GAU) proving grounds showed that the rifle was lighter than the Soviet PTRD by 2.45 kg and the PTRS by 5.58 kg. The German anti-tank rifle still weighed a kilogram more. The Czech rifle was also 60-70 cm shorter than the PTRS and PTRD. Drawbacks included high complexity and much more time required to disassemble the gun, clean it, and reassemble it.

Interesting data was obtained during firing. The muzzle velocity was 1157-1181 m/s and dropped further to 1144-1168 m/s after 80 shots. The German Panzerbuchse started at 1143-1171 m/s and decreased to 1103-1131 m/s 100 shots later. Soviet PTRD and PTRS rifles gave a velocity of 1000-1050 m/s. Simonov's gun proved slightly better.

It turned out that the Czech rifle surpassed its German analogue in barrel life and its Soviet competitors in muzzle velocity. It remained to be seen how muzzle velocity converted into penetration.

Rifle
Bullet and armour
Range (m)
Armour thickness (mm)
Armour slope (deg)
# of shots
# of shots counted
Penetrations
Penetrations (core stuck in plate)
Partial penetrations
Shots fired before trial
Pz.B. M.SS 41
Homogeneous
300
20
20
2
2
2
-
-
15
350
30
20
7
7
7
-
-
17
50
50
0
3
3
-
2
1

500
20
20
5
4
3
-
1
37
600
20
20
5
3
1
-
2

400
30
20
5
5
1
-
4
95
Pz.B. 39
Surface hardened
100
30
20
-
1
1
-
-
-
Homogeneous
300
20
20
Complete penetrations

PTRD
Homogeneous, BS-32 bullet
300
20
20
-
10
9
-
1
-
Homogeneous, BS-41 bullet
350
30
20
-
10
8
2
-
-
PTRS
Homogeneous, BS-32 bullet
300
20
20
-
10
7
-
3
-
Homogeneous, BS-41 bullet
350
30
20
-
10
5
-
4
-

The notes state that "The Czech anti-tank rifle and domestic anti-tank rifles were used to fire at the same plates."

As the trials show, the captured rifle was somewhat better than the PTRS and PTRD at ranges of up to 350 meters, but the small volume of trials don't make this experiment particularly representative. As for larger distances, the testers surmised that the heavier bullets used in Soviet anti-tank rifles would give them the advantage. It's unlikely that this advantage was relevant, as anti-tank rifles were typically used at minimum range to ensure penetration.

T-26, BT-5, and BT-7 tanks with thin armour were plentiful, not to mention thin skinned T-37 and T-38 tanks as well as armoured cars, which would be easy targets for the Pz.B. M.SS 41.

The precision trials gave approximately the same results for all rifles under test. The next stage of trials, the practical rate of fire, was more surprising. Including the time to load a magazine, the practical ROF of the Pz.B. M.SS 41 was evaluated as just 5-6 RPM (assuming that the magazine was loaded when the shooting started). The PTRS achieved 20 RPM and the PTRD 12-13 RPM.

Considering that the Pz.B. M.SS 41 used 5 and 10 round magazines, its rate of fire would presumably be equal to that of the PTRS or higher due to the smaller mass of the rifle and its ammunition. However, it's hard to dispute the values recorded by GAU testers.

Breech of the Pz.B. M.SS 41.

Penetration trials also doubled as reliability trials. The reliability was high. Out of 59 shots there were only 3 jams due to failure to extract. 5 jams were recorded in total out of 145 shots. Inspection of the casings that led to jams suggested that the problem was with the ammunition rather than the rifle, as there was visible corrosion. The jams were not hard to correct with one or two strikes by hand. No other issues were observed during the trials.

As trials showed, the Czech anti-tank rifle with a German cartridge showed high combat qualities. Its penetration was comparable with that of Soviet anti-tank rifles, it was lighter, more compact, and the smaller caliber led to the shooter not tiring as easily. However, while the PTRS and PTRD remained in service until the end of the war, the Germans were already working on new anti-tank weapons for their infantry.

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