Tuesday 26 August 2014

M-17 203 mm SPG

"Conclusions on the factory #172 203 mm self propelled gun M-17

The project proposed by factory #172 consists of a 203 mm gun on the chassis of the mass production SU-152 SPG. The M-17 differs from the SU-152 in the following ways:
  1. Increased caliber (203 mm vs 152)
  2. Increased shell weight (100 kg vs 43.5 kg)
  3. Caseless ammunition
The main components: immobile armour, frame, mobile armour, are all from the SU-152. The gun mount and recoil brake are all effectively the same as on the 152 mm gun, with the exception of an additional casing to prevent separation of seams and the countercoil buffer being replaced with the simplified type.

The gun barrel used is from the experimental 203 mm M-40 gun with the full charge.

Observation devices, controls, fuel system, communication systems, electric components, heating and ventilation systems are identical to the SU-152. In order to reduce recoil, the barrel is equipped with a muzzle brake.

In order to allow for gun depression of -3 degrees, the roof is sloped up by 3 degrees.

16 shells are places in special magazines in the left bay of the fighting compartment. When the magazine is opened, the shell rolls onto the magazine tray under its own weight, from where the loader pushes it into the rammer tray.

The tactical-technical characteristics of the M-17 compared to the SU-152 are shown in the following table:

Characteristic M-17 SU-152
Combat weight, tons 45.8 44.85
Hp/ton 13.1 13.2
Ground pressure, kg/cm^2 0.81 0.8
Armour, mm
Front 60 75
Side 45 60
Rear 45 60
Roof 20 20
Armament 203 mm gun 152 mm gun
Muzzle velocity, m/s 460 650
Propellant mass, kg 8.2 6.8
Shell mass, kg 100 43.5
Gun elevation, degrees 20 20
Gun depression, degrees -3 -3
Ammunition capacity 16 20
Rate of fire per 80 seconds 1 2
Barrel length with muzzle brake, calibers 22.6 46.3
Recoil length, mm 875 850

Upon examination of the project, the following was established:
  1. It is very possible to produce a 203 mm SPG on the SU-152 chassis using factory resources.
  2. High parts commonality with the SU-152 will allow for a rapid production of a prototype with minimal production costs.
  3. In order to reduce weight, reduction of armour thickness is allowed.
  4. The amount of ammunition on board is reduced by 4 shells (16 instead of 20 on the SU-152), which is insignificant, as the power of a 203 mm shell greatly surpasses the power of the 152 mm shell.
  5. A rate of fire of one round every 80 seconds is acceptable for this caliber.
  6. The placement of ammunition in the fighting compartment, convenience of loading, and ramming mechanism are satisfactory, but require testing with a physical prototype.
  7. The mass of 45.8 tons is the limit for this suspension, and the prototype mass should not surpass this limit.
Conclusions and recommendations:
  1. The 203 mm gun on the M-17 greatly surpasses the 152 mm gun in power.
  2. It is reasonable to produce a 203 mm SPG alongside the SU-152 for destruction of highly reinforced enemy fortifications.
  3. The mass of the M-17 SPG should not surpass the mass of the SU-152.
  4. In order to bring the 203 mm gun to self propelled mounts, I consider it reasonable to build a prototype of the factory #172 project with corrections by GBTU USA and provide it for GAU and GBTU trials for a final decision.
Chief of the Self Propelled Artillery Directorate of the GBTU, Engineer-Colonel Alymov
Chief of the 3rd Department of the GBTU USA, Engineer-Lieutenant-Colonel Kovalev
June 24th, 1943"

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