Assuming the sawk has no EVs in defense (most sawks don't, right?), and is has unboosted defense and 31 defense IVs. Also assuming the rampardos has maxed attack EVs, 31 attack IVs, and unboosted attack.
It depends. If Sawk has Sturdy, then no.
If it doesn't have Sturdy:
252Atk Rampardos (Neutral) Head Smash vs 4HP/0Def Sawk (Neutral): 63% - 75% (186 - 219 HP). Guaranteed 2HKO.
If you have Mold Breaker, still, no OHKO.