Whats wrong with russian shells?

Why almost every russian tank with caliber higher than 100mm uses same shell? and why every shell have same pen despite caliber differences. i am talking about 7.7 to 8.3 br

Hmm? Which shells have the same pen and different caliber?

The only tanks in that br range with a caliber higher than 100mm are the IS-4M and T-10M, which are both 122mm.

They fire different shells, with different pen

well i am stupid i thought there is more tanks but any IS shot shells with exact same pen T54 and T44-100

Well in this instance, it is just a coincidence. Br-471 is a fatter shell than Br-412, but fires at a lower velocity. They just happen to balance out for the same pen either way, although Br-471 gets better angled pen and damage.