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Notice that they translated the accuracy data correctly: probable error, not average.
What I like best is that in the source CIA pdf I found that the ballistics is calculated at 760 mm of barometric pressure and +15° C. Which is equivalent to the western (British) naval artillery ballistics standard of sea level and 59° F.
Conversion to the different standart atmosspheric condition is not unusal and can be readily accomplished from the original data.
So then what would the impact velocity be for the BR-412D at 4000 meters when fired at Kubinka's elevation?
Kubinka is at about 200m, so atmospheric pressure is 0.9895 atmospheres. I'm no expert, but I doubt that's particularly relevant.The conversion makes perfect sense if you want to compare the gun to other weapons that are rated for 760 mm of barometric pressure and +15° C.
The Metro US Army standard was 59°F, 750mm Hg, 78% humidity and useduntil 1962. Then the International Civil Aviation Organization (ICAO) standard was adopted by US Army.It is 59°F, 760mm Hg, 0% humidity
Even the soviets would not have issued service firing tables reproducing uncorrected prooving ground data. All data in those pamphlets would be normalized to whatever the standart definition was in terms of ambient atmosspheric conditions and powder charge temperature.While these standart definitions indeed varied from service to service (and sometimes even within a service from time to time), the correlations required to convert one criterium to another standart had been worked out already long before ww1 and posed no difficulties in the 1950´s and 1960´s.
Actually that is not true. The Russians had incorrect velocities in the 122mm BR-471 firing tables as late as 1944. See "Flaws in Russian WW II BR 471 Velocities" at the Axxshistor forum . (Intentionally misspelled because postings with correct spelling are removed).
Notice that terminal velocities are calculated, not actual. The velocity of the projectile while it leaves the barrel can be measured with some precision but not the velocity of a projectile striking the target / or ground downrange. Because the ballistic calculation can only use proxies (as, i.e. shape dependent form factors, metric data to sizes and weights, elevation and corresponding range), the closed form equations employed, contain a degree of error range. Much of the prooving grounds effort was directed to reduce these sources of errors as much as possible.However, transformation of atmosspheric data were relatively straight forward, it was the projectile´s drag characteritics, which created the trouble (f.e. to my memory, relatively subtle changes of the driving bands can have large effects). For the Kubinka tests You discussed, they fired the projectile at close range -and may have controlled the velocity (or not, I don´t know because I haven´t seen the test report)- with a reduced propellant charge -corresponding to whatever their tables attributed as a *calculated* downrange distance, probably rounded up to the next higher impressive number.The downrange striking velocity obtained through these tests is not yet corrected for*atmospheric standart*lower muzzle velocity of the D25 tank gun as compared to the A19 test pieceSuch practices can change the result in order of many hundred meters. However, the firing trials vs armor do not indicate, at least to me, that the soviets also issued wrong service firing tables.
Peter, the penetration table is not from the Soviet manual/handbook, referred to in the CIA report as "Document X". The translated pages from "Document X" only come on page 32 and afterwards.