Yes it is ironic that a man of the cloth developed a weapon of war.
The grenade was detonated when the nose striker hit the ground and was pushed back into the weapon.
To prevent this happening accidentally, a safety pin was inserted through the striker head to hold it out of the weapon.
I can only assume that this pin held the weapons (fins down) in the rack on the fuselage.
The observer/gunner would then remove each pin to allow the armed weapons to fall down and away from the aircraft.