TRICK ANSWER: Just use Stone Edge instead. Even max defenses Shuckle has a chance to be one-shot. With Helping Hand OR Choice Band (effects are interchangeable):
252+ Atk Choice Band Gigalith Stone Edge vs. 252 HP / 252+ Def Shuckle: 216-254 (88.5 - 104%) -- 25% chance to OHKO
Actual answer: With 252HP standard EV's It lives. Even when it has no defense EV's.
252+ Atk Choice Band Gigalith Helping Hand Explosion vs. 252 HP / 0 Def Shuckle: 123-145 (50.4 - 59.4%) -- 80.9% chance to 2HKO after Leftovers recovery
SINGLES (yeahhhh as if it can get Helping Hand, but we're just here for completion):
252+ Atk Choice Band Gigalith Helping Hand Explosion vs. 252 HP / 0 Def Shuckle: 164-193 (67.2 - 79%) -- guaranteed 2HKO after Leftovers recovery
Note that 252 HP is a given for Shuckle. No one in their right mind will run 0 HP EV's on Shuckle. Plus, it won't even be 1-shot with 0 HP, -Def Nature in Doubles.