Thanx, I have the ballistic tables.
At close range the APCR offers a huge advantage.
Depending on the size of the gun (caliber/diameter) the advantage disappears with distance.
I was in error, for the 37mm the advantage disappears at just over 500 meters, not 400.
It means, you can damage or destroy enemy tank from ~200 m with APCR and from ~100m with conventional AP projectile.
At 100 meters these tables (others may differ) show the APCR defeating 64mm of armor compared to 34mm for the standard shot. At 500 meters the difference is 31mm for the APCR to 29mm for the standard shot. What do you think happens at longer ranges?
Nobody cares what happened at longer ranges. If anyone tries it, he is his own enemy.
The 50mm L42 gun crosses over at somewhere between 800 and 1000meters after having a 96mm to 54mm advantage at 100meters.
The 50mm L60 gun crosses over at under 1000 meters after having a 130mm to 69mm advantage at 100 meters.
You can look for yourself at the larger guns for the longer crossover ranges.
Why? Who's concerned?
As Tomo has said, APDS goes the other way. The big difference at close range just gets even bigger at long range. Both projectiles penetrate less at long range but the percentage difference gets bigger at long range.
We are discussing the technology available at the time, not generally the merits of certain projectiles.
As for the 37mm vs big tanks. even at 400meters it was "rated" for 38mm of penetration at 30 degrees from vertical. That assumes a direct hit in the horizontal plane. Also assumes the tank is exactly at the same height and is not tilted (which can help or hurt). If you are plinking away at T-34s from the side you had better be darn close. Note that if you are shooting at the side of the Soviet tanks there is a good chance they have overrun/bypassed you position. If the Soviets return fire with the 76mm guns at under 400 meters it will not be pretty.
Only a suicidal person or a complete idiot would fire armor-piercing projectiles at a moving heavily armored target (tank, assault self-propelled gun) from a distance greater than the direct fire range. At this range, APCR armor penetration usually is higher. Firing tables give armor penetration calculated by a formula with some adjusted coefficients. How close these values were to the real ones is not quite clear.
Nobody is interested in the armor penetration of a 45-mm gun with a solid armor-piercing projectile at 900m - nobody will fire at tanks from this distance, only at unarmored targets or infantry. Only the range of effective fire is important - the distance from which the probability of hitting the enemy becomes non-zero. And it was even less than the direct fire range. It was often the line between life and death for an artillery crew. APCR allowed to gain a couple of hundred meters (for 45-mm) - it was enough to dramatically increase the effectiveness of the weapon, but it required iron stamina and a very competent choice of position for hitting the side projection.
The Soviet firing tables for the 45-mm specified an upper range limit for the APCR of 500m, but this did not mean that beyond that the armor penetration became zero. This was necessary to motivate the crews to spare limited ammunition and not to fire at long range. For the 57mm, the range limit was 1000m, and in both cases the dispersion did not exceed that of conventional armor-piercing projectiles. No one is interested at what distance the velocities of the projectiles or their armor penetration are equal. Only the range of effective fire is important. It determines the combat distance.
It increasingly seems to me that the Soviets came very close to the optimum in their choice of gun parameters, and all alternatives were less effective. The 45/57/76 system for anti-tank and divisional artillery was very effective as long as the quality of the shells was assured. The 45 and 57mm were anti-tank while retaining some effectiveness against infantry, and the 76mm was a versatile divisional gun that provided sufficient effectiveness against tanks. In the course of the war, it may have been worth adding just the 85mm to the anti-tank guns. On the other hand, the 100mm BS-3 anti-tank gun was versatile enough to be used as a corps level gun. A rare case of competence of the Soviet military leadership.