Since the gun of the IS-3 was the already well known D-25, the trials were rather brief.
"During gunnery trials, 37 fully charged shots were fired from the gun.
The recoil length was 520-530 mm, within normal limits.
No malfunctions of the gun occurred during gunnery or mobility trials.
The sight calibration was 2 thousandths off horizontally due to a weakening of the sight attachment screw.
The effort on the elevation mechanism was as follows:
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"During gunnery trials, 37 fully charged shots were fired from the gun.
The recoil length was 520-530 mm, within normal limits.
No malfunctions of the gun occurred during gunnery or mobility trials.
The sight calibration was 2 thousandths off horizontally due to a weakening of the sight attachment screw.
The effort on the elevation mechanism was as follows:
- 0 degrees: 12 kg to lower, 9 kg to lift
- 5 degrees: 13 kg to lower, 8 kg to lift
- 10 degrees: 13 kg to lower, 8 kg to lift
- 15 degrees: 11 kg to lower, 11 kg to lift
Effort on the turret traverse handle when the tank is tilted:
- 0 degrees: 4 kg
- 5 degrees: 15 kg
- 10 degrees: 29 kg
- 15 degrees: 39 kg
The looseness of the gun is 4 thousandth vertically. The looseness of the turret is 6 thousandths horizontally."
The results of the firing were also recorded:
The radius containing the best half of the shells at 1000 meters is 33 cm. The radius containing all 9 shells fired is 40 cm, pretty close. For 2000 meters, the radii are 88 cm and 154 cm respectively. Not too far off from what was observed in the trials for the same gun on the IS-2.
RGASPI 644-2-464