True enough Antonio, on the basic kinetic energy equation. The issue is, and I thought I was clear on, increasing the caliber increases K faster than increasing barrel length. A 40% increase in shot size will increase the mass by a factor of 3, than 30% will double it. Contrariwise, increasing barrel length does not result in proportional velocity increase, except in rather small calibers. (Still 73 calibers is an impressive barrel length.) That is why increasing caliber gets results faster than lengthening the barrel.
Navies have known that principle for centuries. That is why carronades were developed, and why 11 inch guns were more useful than longer 8 inch guns. WW1 brought the penetration problem onto land. That energized the bore vs. length problem. Bigger shots make much heavier guns, longer barrels make less heavier. As such the maximum practical size of an AT gun became 75mm/3inches or so. Both the 88 pack 43 and Soviet 85mm were to big for their crews to manhandle. The Soviets solved their problem with a little motor unit, the Germans didn't last long enough to come to a solution.
The APCR round you reference was not available in til October of 1944. So it wouldn't be available in any of the eastern front games currently in publication. The Russians seem to have lied about the statistics anyway. Post war evaluations put the APCR penetration at a little over 120mm, which is still pretty impressive. Of course we never lied about specifications like that, such as belt armor on battleships?
Oh yeah, I know about the LL's, the L's and the
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Larry, I haven't seen any numbers on the T34/57. The references I have seen in the past few days only say "very few". The ZIS-30 does seem to have had over 100 made. Since the Soviets made over 115K tanks, assault guns, and so forth, it amounts to little more than a pilot run. I haven't gotten a picture yet. I expect it would look like the M2/M5 Cleatrak, but better balanced, and obviously easier to build.