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Unlucky 45 mm

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By the end of 1941, it was clear that the power of the main Soviet anti-tank gun, the 53-K 45 mm mod. 1937, is insufficient to combat new variants of German tanks, which had thicker armour and applique plates. In addition, Soviet intelligence reported that Germany was developing vehicles with even thicker armour. The replacement or modernization of the 45 mm gun was a very pressing issue at the start of 1942. One of the candidates for the new role was the M-6 45 mm anti-tank gun.


A  meeting of the Artillery Committee of the Main Artillery Directorate was held in January of 1942 to discuss the development of anti-tank artillery. The result of the meeting was the development of new tactical-technical requirements for a 45 mm gun, with the requirement that the new gun must be as similar to the current one as possible. The requirements were sent to Molotov (the name of Perm in 1940-1957), to Molotov factory #172, which produced 45 mm mod. 1937 guns.

Soviet soldiers preparing to open fire from a 53-K 45 mm mod. 1937 gun. Kalinin Front.

Two bears in one cave

Factory #172 had two independent design bureaus: the factory's artillery design bureau KB #172, directed by S.P. Gurenko, the factory's chief engineer, and the "science prison", the special department of the NKVD's 4th special department at factory #172 (OKB-172), which was headed by N.A. Ivanov with M.Yu. Tsiryulnikov as the technical director. Both design bureaus got to work, designing two weapons: design bureau #172's M-6 and OKB-172's M-42.

The more fortunate of the competitors, the M-42, was covered in another article. Let us speak of the brainchild of design bureau #172.

A meeting was held at KB #172 on February 20th, 1942, which decided the direction the design of the new 45 mm gun will take. The simplest solution was obvious: to install a new barrel on the same mount. However, a decision was made to not stop there, but also consider the ease of production in wartime. An idea came up to simplify the mount and reduce the number of parts involved, cutting down the time it would take to produce by 30-40%. The design bureau's engineers tried to do two things at once: increase penetration and the volume of production. After this meeting, the following features for the new gun were confirmed:
  • A new barrel, longer and simpler due to simplified holds.
  • Simplified breech without the inertial safety and a number of other changes.
  • The existing semiautomatic mechanism with several simplifications.
  • A new lengthened cradle with thicker sides, largely the same as the one in production.
  • Existing recoil mechanism.
  • Upper mount: new, without boxes for the elevation and traverse mechanisms, stamped and welded, radically simplified.
  • Lower mount: largely the same as the existing one, with simplifications.
  • Elevation mechanism: screw type instead of half-round.
  • Trails: existing with minor simplifications.
  • Axle: existing.
  • Shock absorbers: new, significantly simpler, and modified for the increased weight.
  • Wheels: existing.
  • Shield: new, simplified, 7 mm thick. The middle part was stationary, the upper part flipped up.
  • Sight: existing.
All changes were to be introduced in such a way that the existing instruments and equipment would not have to be changed. All work on the project was supposed to involve technologists at every level. Two prototypes were to be built using existing equipment in order to simplify the adoption into production. The chief engineer and chief technologist were equally responsible for the blueprints.


M-42 gun in combat and transport position.

A GAU meeting was held at factory #172 in early March of 1942 on the issue of producing 45 mm guns to new requirements. Three projects were reviewed:
  • M-42 designed by OKB-172
  • M-6 designed by KB #172
  • 104-K designed by factory #8
The M-42 prototype was already done, but the M-6 was not yet built. The 104-K designed on the factory's initiative back in the summer-fall of 1941, was still being worked on. After a report on each gun was heard, the representatives from the factories squared off. It was necessary to determine which variant to focus efforts on.


Weight distribution of the M-6 45 mm gun.

The 104-K was rejected for a number of reasons. It was pointed out that a brand new anti-tank gun, designed for a 920 m/s muzzle velocity, was significantly different from the existing gun in every way, including the semiautomatic breech.

The ammunition was also original: the shell was taken from the 53-K, but the casing was used from the experimental 45 mm 49-K autocannon, which was not adopted into service. The adoption of a new type of ammunition in parallel with the existing one would have inevitably complicated the army's supply situation, and rapid production would not be possible in wartime conditions.

The conclusion was obvious: the 104-K would take a long time to enter production, and its complexity compared to the 53-K would result in a decrease in production volume.


M-6 from the rear.

The M-6 and M-42 were considered promising. It was decided to expedite the trials of the M-42 prototype. As for the M-6, two prototypes were due by March 25th: one with the M-6 oscillating part on the stock 53-K mount, the other on the new simplified mount.

In addition, the ballistics of the M-42 and M-6 were to be unified. Since trials of the experimental M-42 barrel have already been completed and showed good results, the barrel of the M-6 was extended by 85 mm.

Trials of the M-6

The first prototype of the M-6 was ready by early April of 1942. It had its own ballistics, as its barrel was shorter than that of the M-42. Factory trials began immediately. On May 21st, the weapon was sent to proving grounds trials in Sofrino, but the proving grounds were not ready. Trials had to be done as quickly as possible, so an order on May 28th, 1942, moved them to factory #172's proving grounds and the GAU's Ural proving grounds in Nizhniy Tagil.

Blueprints of the M-6 barrel.

Since the first prototype of the M-6 departed for Sofrino and was left there (it's likely that this gun is now on display at the Central Museum of the Great Patriotic War in Moscow), prototype #2 was prepared for trials. It was built to specifications of prototype #1, but had a longer barrel. A number of additional changes were made: the impact stroke of the leaf springs was increased, and the recovery stroke was reduced. The sliding breech weight was reduced to that of the stock 53-K. The inertial body of the breech was made heavier, and the recoil springs were weakened to reduce over-returns.

Prototype #2 was tested at the factory by towing and firing. 80 shots were fired, 29 of them with increased propellant. The gun was towed for 300 km over various roads. The towing speed was 25-35 kph on good roads and 10-15 kph on poor ones. As a result, the factory decided that the gun was ready for battle and had satisfactory characteristics. The ballistics of the gun were the same as those of the M-42. The conclusion was: "The gun passed factory trials and is being presented for proving grounds trials."

M-6 prototype #1 in battle position.

Proving grounds trials of the M-6 were finished by June 25th, 1942. The goal of the trials was to evaluate the characteristics of the gun, ensure robustness of the main components, and determine if the modernized components could be launched into production. 950 shots were planned, 600 of them with increased propellant on concrete with the trails braced against wooden beams. The robustness and stability of the gun were evaluated. In addition, it was necessary to test the M-6 by towing it for 1000 km over various roads. In actuality, the gun fired 969 shots and travelled for 1063 km.

Technical description and characteristics

The M-6 is a semiautomatic split-trail gun with an upper mount that shifts on top of a lower mount. The barrel is a monobloc with a return mechanism. The breech is vertical, sliding, semiautomatic. The breech unlocks and ejects the spent casing at the end of the recoil cycle. The breech locks automatically when the next round is chambered.

M-6 prototype #1 in combat position, viewed from the side.

The gun mount consists of a cradle with recoil dampening mechanisms, upper mount with the aiming mechanisms, lower mount with the split trails, sprung axle, wheels, and shield. The recoil mechanisms are placed into the cradle, under the barrel, and consist of a hydraulic recoil brake and a return spring. The recoil length is 620-780 mm.

The aiming mechanisms are attached to the upper mount. Both the traverse and elevation mechanisms are of the screw type. The sight carrier is attached to the left side of the mount. The sight is linked to the barrel with a parallelogram ball and socket linkage.

The lower mount is connected by a ball and socket joint to the lower mount, which ensures the proper positioning of trails on uneven terrain.

Each trail extends by about 34 degrees. The split trails are not connected to the axle. The leaf springs are engaged automatically. When joined, the trails grasp the axle and result in a rigid connection between the axle and the lower mount. The horizontal aiming arc with extended trails is about 60 degrees.

M-6 prototype #1 in travel position with the shield folded down.

A 7 mm thick armoured gun shield protects the crew from bullets and shrapnel.

The characteristics of the M-6 are as follows:
  • Caliber: 45 mm
  • Muzzle velocity: 335 m/s (HE) 885 m/s (AP)
  • Maximum range of an HE shell: 4670 m
  • Barrel length: 69 calibers
  • Number of rifling grooves: 16
  • Type of rifling: constant at 7°9'45''
  • Depth of rifling: 0.5 mm
  • Width of rifling: 6.5 mm
  • Width of rifling groove field: 2.5 mm
  • Elevation: from -5 to +25 degrees
  • Rate of fire: 25-30 RPM
  • Elevation flywheel effort: 3 kg
  • Traverse flywheel effort: 5 kg
  • Bore axis height: 711 mm
  • Maximum length: 5043 mm
  • Wheel base: 1400 mm
  • Maximum height with gun level: 1160 mm
  • Shield height: 1160 mm
  • Clearance: 260 mm
  • Mass in combat position without accessories: 600 kg
  • Barrel mass: 156.2 kg
  • Breech and semiautomatic mechanism mass: 13.3 kg
  • Mass of the upper shield: 65 kg
  • Mass of the lower shield: 17 kg
  • Mass of the cradle and recoil mechanisms: 68 kg
  • Mass of the oscillating part: 225 kg
The ballistic qualities, design, weight, and usage characteristics of the M-6 were compared with those of the M-42 and 53-K. Upon completion of the trials, it was concluded that:
  • The M-6 gun passed gunnery and mobility trials.
  • The M-6 gun did not pass stability trials when firing from concrete.
  • The ballistics of the M-6 are identical to those of the M-42 and the guns only differ in the design of their components.
  • Temporary reduction of production is possible when changing over from the 53-K to the M-6, which is unacceptable.
  • The issue of improving the ballistics of the 53-K is already solved by the M-42.
  • The M-42 allows the resolution of the issue of rearming the Red Army only by replacing the barrel and insignificant changes to the mount.
  • The M-42 gun does not resolve the issue of simplifying production. In addition, the M-42's barrel is harder to make than the 53-K barrel.
  • The M-6 gun solves both the issue of improving ballistics and, after it is implemented in production, increasing production quantity.
Quality vs quantity

With identical ballistic characteristics, the M-6 gun was easier to produce than the M-42. However, if accepted into production, the output of 45 mm anti-tank guns would drop for some time. These losses would be later compensated by larger numbers, but this was unacceptable in the summer of 1942, even for a short time. 


M-6 gun towed by a GAZ-AAA truck with and without a limber.

As a result, the M-6 gun remained an experiment. It is known for certain that two prototypes and a small batch were produced. After their failure in the summer of 1942, factory #172 made two batteries of the M-6 (numbers 101 through 109). Four of them went through trials at the ANIOP in February of 1943, and army trials in March. The results were no better than in the summer of 1942. The guns were returned to the factory with proposals for improvement.

In August of 1943, it was reported to the Chairman of the Artillery Committee, V.I. Hohlov, that factory #172 improved the blueprints of the M-6 and modernized one prototype. Based on this, it was proposed that further trials be performed, and a decision made regarding the possibility of mass production. However, the M-6 was no longer relevant.

Five M-6 guns with improvements made after the trials remained at the factory in December of 1943. One of them had a simplified semiautomatic mechanism, which was introduced into M-42 production. They passed factory gunnery and towing trials. The factory asked the GAU to tell them where to send the guns. It was proposed that they be sent to the ANIOP or other proving grounds to perform lifespan trials.

Interestingly enough, in such a heated wartime battle, a more complex gun won out. The decision that was rejected by engineers of factory #172, but developed by OKB-172, managed to be more viable. The better choice is not always the necessary one.

A walkaround of the prototype M-6 gun can be seen here.

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