It is impossible to pierce anything with a B1 (apart from light tanks) because a 75mm gun with disastrous penetration and ballistics, I did some research on the gun and the shells used, he says a lot of thing but does not speak of penetrations so I deduce that the one chosen by Gaijin and be false be he has access to documents that I do not know. However, it is very similar to the 75 mle 1897 gun. In all guns, the 75 gun is seen to be a wonderful anti-tank weapon, it was even used by the Germans during the Battle of France. to deduce that it had good anti-tank shells (and therefore shells that could penetrate the thickest armor for the time), this gun was also used as anti-tank guns in barracks on the Maginot line. Gun used in the navy, in short a good anti-tank gun theoretically.
As for the 47mm gun, it was literally intended FOR anti-tank use, it is even described like this "Its ballistic qualities, both in precision and in perforation capacity, make it one of the best guns most powerful of the time, capable in particular of destroying all the tanks then in service. and here it is technical capacity:
The 47 mm armour-piercing projectile (47 × 380R) model 1936 has a mass of 1.726 kg and an initial speed of 855 m/s.
French tests it pierces 106 mm at 100 m, 89 mm at 500 m, 72 mm at 1,000 m, 57 mm at 1,500 m under 0°.
German tests give 57 mm at 100 m, 50 mm at 500 m, 42 mm at 1,000 m and 36 mm at 1,500 m under 30°
At 30° at 100m 47mm, 500m 38mm, 1000m 29mm,1500m 22mm.
At 0° at 100m 59mm, 500m 47mm, 1000m 36mm, 1500m 27mm
So be Gaijin (and I’m leaning towards this hypothesis) we voluntarily Nerf this Shell (so is this gun) which would be unfair or he has access to docs of which I do not have knowledge.