When the monster equipped with “Big Bang Shot” is destroyed, and “Big Bang Shot” is destroyed as a result of this, the equipped monster is not removed from play.
The effect of “Big Bang Shot” that removes the equipped monster from play can be resolved between steps of a chain. For example, if “Change of Heart” targets a monster equipped with “Big Bang Shot”, and “Mystical Space Typhoon” is chained to “Change of Heart” to destroy “Big Bang Shot”, first resolve “Mystical Space Typhoon” and destroy “Big Bang Shot”, then remove the monster that was equipped from play, and THEN resolve “Change of Heart” (and the effect of “Change of Heart” disappears).
If a monster equipped with “Big Bang Shot” is flipped face-down, it is no longer a target of “Big Bang Shot” so “Big Bang Shot” is sent to the Graveyard and the monster is not removed from play.
When “Imperial Order” is active, and you destroy “Big Bang Shot” with “Dust Tornado”, the effect of “Big Bang Shot” that would remove the monster from play is NOT applied.
When you send “Big Bang Shot” to the Graveyard with “Emergency Provisions”, the monster is removed from play at the same time.
When equipped to “Guardian Ceal”, if you send “Big Bang Shot” to the Graveyard as a cost for “Guardian Ceal”’s effect, “Guardian Ceal” is removed from play but “Guardian Ceal”’s effect still resolves.
If a monster is equipped with “Big Bang Shot” and “Fiber Jar” is activated, both “Big Bang Shot” and the equipped monster are shuffled into the Deck, and the equipped monster is not removed from play even though “Big Bang Shot” was removed from the field.
If you equip your “Big Bang Shot” to your opponent’s “Dark Magician”, and “Dark Magician” attacks your “Giant Soldier of Stone”, the opponent of the owner of the “Big Bang Shot” takes the damage (so your opponent, who attacked with “Dark Magician”, takes 900 points of damage.)
The battle damage caused when the equipped monster attacks a Defense Position monster is considered to come from the equipped monster, not from “Big Bang Shot”. So a “Don Zaloog” equipped with “Big Bang Shot” could still make the opponent discard 1 card when attacking a face-down monster with low DEF.
If you Special Summon a monster with “Premature Burial”, and equip it with “Big Bang Shot”, and “Heavy Storm” is activated, the effects of “Premature Burial” and “Big Bang Shot” form a chain, with the controller of the 2 cards determining the order in which they are placed on the chain, and the order in which they are resolved. If the controller chooses “Big Bang Shot” to be Step 2, then the monster will be removed from play. If the controller chooses “Premature Burial” to be Step 2, then the monster will be destroyed and sent to the Graveyard.