And shot at. CAMD RF 38-11369-64 tells us why:
"Trials of the tank turret by shooting
The tank's armour was tested with mount testing shells, in order to find out the reliability of the optical sight and its mounts.
Factory #100 performed a shelling of the tank with armour piercing shells in order to determine the reliability of various components of the tank. At the same time, this was used by our commission to test the sight.
The IS turret had a new 4x sight installed and carefully calibrated.
The tank as shot at with a 76 mm ZiS-5 gun from a distance of 300 meters. 10 shots were fired, 5 shots with mount testing shells, and 5 shots with armour piercing shells.
The mount testing shells were aimed at the area of the sight, with two shells impacting the shell on the level of the sight, and three in the mantlet on the same plane.
The armour piercing shells were used to test the sturdiness of various parts of the tank (driver's hatch, commander's cupola, etc). The hits were as follows:
- Driver's hatch: one hit
- Front armour: two hits
- Commander's cupola: two hits"
- The sight was free of deformations and defects.
- Sight adjustment and sharpness did not suffer.
- Calibration of the sight was not knocked off.