For example, at 1500 meters range, the tank may occupy a 2 degree field of view.
Mighty big tanks they have in your part of the world if they subtend 2 degrees (over 35 mils) at 1500 metres. The Ratte could at an appropriate angle, but the Karl Mörser is too small. Using mils for subtenses makes more sense, and I don’t know of an army that doesn’t.
There are a lot of things to consider with these oblique shots. For example, penetration is lost as the round slides along the side armor plate, the more efficient the ballistic coefficient of the penetrator, generally the less likely that the penetrator is to initiate penetration at extreme oblique angles. The rate at which the penetrator loses effectiveness will increase as the length of the penetrator increases relative to its length.
Eh? What does the length of the penetrator have to do with this? Nose shape, yes, there’s a bunch of mysterious stuff going on there that no simple formula is able to capture, and there’s the question of piercing caps, but I don’t see what penetrator length has to do with it. Pray explain yourself.
If the penetrator is a HEAT round, at such oblique angles, the formation of the cone will be severely deformed, radically reducing the effectiveness of the round.
It’s not jet formation that is the problem so much as fuze initiation. HEAT has to use point initiating, base detonating (PIBD) fuzes, because the penetrator needs to start forming at a reasonable stand-off distance, but to do this the warhead needs to be initiated at its base. Obviously there are some values of impact angle, probe length, and calibre for which the shoulder of the round will strike the armour before the tip of the probe does, and I doubt there will be any result from that other than a ricochet by the ballistically squished remnants of the projectile. One approach, as used in the Swingfire ATGW, is to use a nose cone (actually an ogive rather than a cone) consisting of two slightly-separated layers of copper. When the nose is deformed by impact so that the two layers are in contact, an electric circuit is made which initiates the warhead. On Swingfire this worked up to 80 degrees obliquity, and at that angle the line-of-sight distance through the armour seen by the penetrator is 5.75 times its normal thickness. Line-of-sight thickness is not a bad estimator of armour basis for HEAT, as the penetrator is moving at such high speed that target density matters a lot more than target strength.
Of course, not a problem for Les’ chosen period of France 1940 except for the special case of the No. 68 Grenade.
All the best,