Wednesday 4 May 2022

SU-152 Practical Accuracy

The topic of accuracy and precision of Soviet guns comes up a lot. Stereotypically, these guns are depicted in media as being unable to hit the broad side of a barn. Records of trials show otherwise. Here is a record of one such trials at various distances.

Unfortunately, the dispersion isn't nicely mapped out like in other trials, but we can use the known diameter of the hole (152 mm) to estimate it.

First, 200 meters. The rounds are closely clustered together inside the bullseye. Its radius can be estimated at 2 and a third calibers, or 350 mm. At this range a SU-152 gunner can hit any target without difficulty.

At 400 meters the majority of the shots are still in the bullseye (with three right on top of each other), but one went wild. It landed 5.5 calibers or about 83 cm away from the point of aim. Not great, but still good enough to hit a tank-sized target. The clustering in the center means that the gunner is still more than likely to hit whatever point they were aiming at.

Results at 600 meters are a little bit scattered. There's still a larger grouping and an outlier like before. Either way, the hits are no more than 4 calibers or 61 cm away from the point of aim, hitting a tank sized target without issues. From this range the gunner is less likely to hit a particular part of a tank like a vision slit, but with a 40 kg AP shell you don't need to.

As can be expected, the dispersion grows at 800 meters. The furthest hit is 8 calibers (1.2 meters) off the center. This is still close enough to the center to hit a tank sized target, but there is now a noticeable chance of hitting the edge rather than the center. If only a part of the tank is exposed rather than the entire silhouette, it's possible to miss.

These results aren't outliers. Here we see the results of trials held on February 3rd, 1943. The right grouping was achieved while firing at a range of 500 meters. The results are similar to what we see in the 400 meter and 600 meter trials above: four shots right on top of each other with one outlier.

The left grouping was achieved from a range of 1000 meters. The grouping seen here is actually tighter than the one above, although it's impossible to tell where the gunner was aiming (since the target was reused for the two groupings). If we take the 800 meter trial and try to determine precision rather than accuracy, we can see that the outermost shots end up within 2.5 calibers or about 38 cm of the center of the group.

That's still worse than a result in the 1000 meter trial, but comparable. Knowing the offset of his gun at this range, a skilled gunner would still be able to make an excellent shot with the 152 mm ML-20S gun-howitzer.

1 comment:

  1. But wasn't the intended tactical use of AFV fielding this gun (SU-152; ISU-152) supposed to be in providing overwatching supporting fire at ranges as great as 1500-2000 meters? At that range, a miss on a tank-sized target is definitely possible (against soft targets it's probably still quite effective).

    At the slow reload speed, a tank target may have ducked back under cover.

    That's why I have always been a bit puzzled that ISU-122 production was discontinued postwar, but ISU-152 production and use continued, plus the object 704 intended to replace it also carried the ML-20. Accuracy at these ranges isn't a problem for the A-19/D25-T. Or even better, the 130 mm naval gun. And they all would still pack a powerful HE round punch.