Oreshnik was originally designed to deliver nuclear warheads.
The Oreshnik launch that succeeded contained "dummy" warheads that exactly matched (size, weight & balance) the nuclear warheads.
The conventional warheads would certainly match the exact size and weight of the nuclear warheads.
However there probably is an issue with the CG of the conventional warheads not exactly matching the CG of the nuclear warheads.
I would not want to be a ruzzian rocket scientist if (when) the next Oreshnik launch fails.
CG ???