As with most of these things, this doesn’t actually work. Antimagic fields suppress magic inside them, they don’t dispel it. So the bullet would be unshrunk while inside the field (and the field would affect the bullet while it’s still inside the gun’s barrel, so that would turn out really badly) and then instantly shrink again as soon as it exits the field.
Ironically, this is actually just an overly complicated way to do something the spell alone can achieve. You can end shrink item with a command word from the caster. It would require two people working together, but if the caster readies to give the command immediately after the gun is fired, the bullet would be unshrunk midflight and have the desired effect!
As with most of these things, this doesn’t actually work. Antimagic fields suppress magic inside them, they don’t dispel it. So the bullet would be unshrunk while inside the field (and the field would affect the bullet while it’s still inside the gun’s barrel, so that would turn out really badly) and then instantly shrink again as soon as it exits the field.
Ironically, this is actually just an overly complicated way to do something the spell alone can achieve. You can end shrink item with a command word from the caster. It would require two people working together, but if the caster readies to give the command immediately after the gun is fired, the bullet would be unshrunk midflight and have the desired effect!