On the other hand,when i try using Russian arty BL,i never get such a hits :/
You just need the inverse of the RNG you had against the LeFH.
Seriously though, I have actually had great results with the ML-20, but only so long as the axis have all chosen commanders that can't recon and bomb the onmap. Last I used one I was able to murderface OKW medic trucks like nobodies business. The ML-20 is surprisingly ineffective against Ostheer because you don't need an artillery piece to wipe their squads and team weapons. Katyusha does everything the ML-20 can do against Ostheer, but for cheaper, as a stock option, and with more consistency.
It's been a while since I've used an ML-20 now that I think about it though. Depending on how the war vs FRPs goes, chances are I won't for a long time either.