"Conclusions on the report on firing the M7 gun on the American M10 SPG
The GBTU Chief and GBTU SPG Directorate instruction #149068 issued on October 18th, 1943, by the GBTU proving grounds (Kubinka railway station, Western railway) conducted trials of the M7 gun installed in the American M10 SPG. According to the trials program, the following characteristics of the gun were to be recorded:
- Size:
- Barrel length (total)
- Rifled section length
- Diameter between opposing grooves and between opposing lands
- Land width
- Chamber size
- Shell and casing size
- Ballistic data:
- Pressure
- Muzzle velocity
- Maximum range
- Precision
The proving grounds did not record the most important ballistic data (muzzle velocity, maximum pressure, maximum range) and dimensions (diameter between grooves or lands, land width, chamber size), as as result of which the tactical-technical data provided in the report does not give characteristics of the gun.
The description of the sights and their tactical-technical characteristics is absent completely.
The characteristics of the M62 shell are clearly distorted. The proving grounds describes the shell as "solid shot with a ballistic cap and a pressed in tracer" whereas it clearly has a chamber for explosive filler, a screw-in tracer, and both an armour piercing and a ballistic cap.
The ability of the M62 shell to penetrate a Ferdinand SPG or Panther tank was not determined.
The proving grounds merely recorded the results of firing at a Ferdinand SPG and a Panther tank without determining the maximum range at which penetration can be achieved.
The results of firing on the Ferdinand hull presented in table #6 contain an inexplicable paradox:
- Firing at the side of the Ferdinand SPG at a range of 100-150 m at 90 degrees the shell makes a 70 mm deep dent.
- Firing at the side at a range of 700 meters at an angle of 65 degrees results in penetration 100% of the time.
No conclusions regarding the penetration were made. Practical trials of the M62 shell's maximum penetration were not conducted.
The report is closer to an elementary description of the vehicle and its gun than a trial of the gun.
This leads us to believe that the trials were conducted improperly, the results are not reliable, and the trials need to be repeated.
Senior Assistant of the Chief of Department #2, GBTU USA, Engineer-Major Karelin
Senior Engineer, Department #2, GBTU USA, Engineer-Captain Ivanov"
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