Meet the Zveroboy (Beast Slayer)!
The two were very effective in combat. Very.
Originally designed as breakthrough self-propelled guns, they were equipped with massive ML-20 152 mm howitzer, without any AP shells. They were extremely successful at their designated role, thanks to their massive caliber and good mobility.
Although it had insufficient armor, and a very bad rate of fire, it proved to be an extremely deadly ersatz tank destroyer, all thanks to its massive shell. Though it had a lower kill reliability than a successfully penetrating shell, it was massively dangerous to German heavy tanks like the Tiger, able to blast their turrets off using blast alone.
If it hits an armor plate and failed to penetrate, it would absolutely destroy the plate, and if it hits the turret it shears it off completely. Used in mass ambushes, they are one of the most effective heavy tank killers of the war.
Edit: Tanks destroyed by it