And there aren't so much mons with access to Punishment, actually. In the OU environment... only Infernape. Assuming a, for example, +3 Calm Mind Reuniclus and a common Nape:
Infernape@Life Orb (252 EVs, Neutral Nature) 120 Punishment vs Rankurusu@Leftovers (252/252 EVs, Neutral Nature): 65 ~ 76,8% (276 ~ 326 HP).
But maybe Weavile thanks to STAB and the freedom of switching on to a psychic move...
Weavile@Life Orb (252 EVs, Neutral Nature) 120 Punishment vs Rankurusu@Leftovers (252/252 EVs, Neutral Nature): 108 ~ 127,3% (458 ~ 540 HP)
Hmm... weird, but interesting.