Something might be wrong with Dauntless Shield, doesn't seem to be applying Defense buff in Damage Calc
+3 252 Atk Zacian-Crowned Close Combat vs. +1 252 HP / 180+ Def Zamazenta-Crowned: 464-546 (119.5 - 140.7%) -- guaranteed OHKO
Possible damage amounts: (464, 468, 474, 480, 484, 490, 496, 502, 506, 512, 518, 524, 528, 534, 540, 546)
This is with Dauntless Shield
+3 252 Atk Zacian-Crowned Close Combat vs. +1 252 HP / 180+ Def Zamazenta-Crowned: 308-364 (79.3 - 93.8%) -- guaranteed 2HKO
This is without Dauntless Shield, but +1 Defense