Yeah you’d have to take bullets and magically grow them, and move the anti-magic ring so it covers the breech to the muzzle. Would be quite a hassle to carry the spare ammunition though.
Edit: Actually you could keep the spare ammunition in a pouch attached to the gun inside the radius of the ring. Just make sure it doesn’t fall out.
DM: Oh no. You ruined my campaign!
Another player: Wouldn’t the canonballs just shrink again once they leave the antimagic field? It wasn’t permanently dispelling the magic locks.
DM: Shhh!
Yeah you’d have to take bullets and magically grow them, and move the anti-magic ring so it covers the breech to the muzzle. Would be quite a hassle to carry the spare ammunition though.
Edit: Actually you could keep the spare ammunition in a pouch attached to the gun inside the radius of the ring. Just make sure it doesn’t fall out.