Thursday 19 May 2016

IS-3 Gunnery Trials

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:
  • 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


  1. Unlike the earlier test there is more vertical dispersion than horizontal dispersion.

  2. The dispersion is only fair. If you compare it to the British 17pdr which works out to a 50% dispersion on ~71cm at 2000yds or ~79cm at 2000m.

  3. For those who are more familar with statistical terms,
    the data translate to:
    mean dispersion: 0.32m
    standart deviation: 0.095m
    mean dispersion: 0.92m
    standart deviation: 0.362m

  4. The mean dispersion figures are incorrect. The russian data refer to "RADIUS" and not "DIAMETER".
    Thus, "mean dispersion" at 1000m would be 0.64m (1.84m at 2000m) and the "std. deviation" becomes probable error instead.

    1. The word "diameter" does not appear in the article. You are mistaken.

  5. Your source INDEED refers to "radius", as I claimed, and not "DIAMATER". This is important once You start to compare figures with other sources, particularely with german sources because You cannot easily declare a Radius figure (soviet) similar to another figure which more closely resembles a "diameter" (german) .

    Additionally, as I responded to "anonymous", his dispersion figures actually respresent not mean dispersions but probable errors (1/2 mean dispersion) because the mean dispersion is calculated against the diameter or the zone (if x and y are not of equal size), and never against the radius. Since the radius is only 1/2 the diameter, it´s legitimate to consider the soviet data releveant only for the probable error.

    I hope You understand also that RADIUS is not a rectangle. Radius measures from the centre to an edge. Readers more familar with the matter have noticed already that german fire effect sources give the constructive rectangle and reproduce their full extant (zone).