The terminal velocity relations for 100mm come directly from ARTKOM GAU and are to be used as reference for describing distances (AP projectiles explicitely mentioned) after trial. In such more experimental trials, unlike in field trials, f.e., the actual terminal velocity was carefully measured after each shot on a test range with calibrated instruments. The gun was not put at a distance but the charge was modified to obtain a desired striking velocity. Ranges then were calculated based upon ARTKOMs velocity tables used for reference. This is what carries significance for this primary source document, because it explecitely testifies which range / velocity combinations were officially specified by ARTKOM in this period.
It is important to understand the form, in which distances are presented. After all, ARTKOM gave the remaining velocity by a table (sometimes by a formula), which it clearly stated in its official documents. Its not needed to interprete anything here, such information would lead a commander to assume he could defeat a given target, at say 1000m. I believe, they all thought so. Yet, ARTKOM didnt make clear that the actual velocity / distance relation for its reference was above the specification requirement for projectiles actually procured for service, and this resulted in a distance of a couple of hundred meters less for a given downrange velocity. Zaloga and many writers cited and continue to cite these trials unreflectedly, and I think even Bird/L. worked using the hypothesis that official distance data from actual soviet trials 1944-1945 bear close relationship to real terminal velocities. It is submitted here -as my personal opinion-, that the discrepeancy is large enough to not just constitute a minor problem for modern re-assessments of vintage period armor trials.
Of course, we do not know who was responsible for this error but it is necessary to be careful when actual terminal velocities are omitted from soviet trial data of the period 1944-1945. Distance data only are knowingly compromised and thus, may be a misleading proxy. Equally, one needs to be careful when the actual way the trial was staged is unspecified. Was the charge modified to obtain a desired striking velocity? Was the gun moved away the distance, instead? These two forms are not necessarely as compatible with each other as one might assume. Ambient temperature is relevant, as well as target condition, too, on how the armor responds.
There is a difference between correlating factors and prediction. Its fairly easy to establish correlations between known datapoints but it will be difficul, too, to also predict unknown datapoints from the isolated sample of known datapoints. Since this sort of AP- vs Armor discussion revolves around historical data, of which the vast majority is either incomplete, unknown or lost, one has to eventually take the step to move away from closed form equitations. Its necessary to adopt a statistical inference, which takes into account and embraces the fact, that we can update our information and challange prior assumptions. This is better reflected, I think, in adoption of bayesian statistical modelling. This way, we probably cant pinpoint a discrete result or predict every event but we can exclude the unlikely...Is it even possible to predict the interaction of shell and armour at high obliquity with so many variables affecting the results? Clearly there has to be some limits on what is possible, otherwise we would've seen photos of the UFP of KT penetrated by the soviet 45mm gun.
Is there really no lower limit on protection provided by the sloped armour (besides that it cant be less than its nominal thickness, obviously... right? at this point it wouldn't surprise me to learn that even this is not true.)
Once the plastic deformation exceeds a limit and becomes a permanent change of geometry, work hardening sets in. Work hardening increases the strain limit, but does not increase the limit of plastic deformation. Quite contrary, a high degree of plastic deformation work hardening can increase the brittle tendency due to triaxial stress risers, locally defeating the limit of plastic deformations. When this happens, one can frequently observe crack formation between two or more of the nearest boundaries (hole or plate edge). Further, the resistence to perforation is reduced by closeby boundaries (unsupported right angles and holes).Have you considered that the armour remained ductile because its structure was already compromised by a nearby hole, therefore it didnt offer as much resistance to the 152mm shell and did not absorb as much energy as an otherwise intact plate would've?
Thats why a 3 cal minimum distance between two impact points was specified in the first place in trials to allow only "fair hits". For the 152mm, this would require 0.46m distance to the next impact to be free of edge effects and cracking. Only a very ductile plate may not show brittle tendencies despite multiple, closeby impacts, and this is shown here, despite the largest possible calibre (152mm), wich constitutes the most severe form of test for ductility. It goes some way to directly contradict the interpretation of brittle behavior of german plates if engaged by large calibre AP, found in the article, no?