It could be under the barrel and a few inches forward, like on the end of a bayonet.
The ring placement isn’t the problem. Its the rings effect on the cannon ball returning it to normal size.
There’s a reason today we don’t use a few grams of gunpowder to shoot a cannon. The mass of the 5lbs cannon ball is far greater than the energy produced by expanding gasses of a few grams of burned gunpowder. So with a 5lbs cannon ball essentially magically appearing right at the mouth of the barrel (because the ring’s effect), it effectively is a plug plugging up the barrel entirely.
It could be under the barrel and a few inches forward, like on the end of a bayonet.
It would have to be well calibrated, but it’s possible depending on the rules of the ring.
You’d still have other issues around mass and size, but gun configuration could be solved.
The ring placement isn’t the problem. Its the rings effect on the cannon ball returning it to normal size.
There’s a reason today we don’t use a few grams of gunpowder to shoot a cannon. The mass of the 5lbs cannon ball is far greater than the energy produced by expanding gasses of a few grams of burned gunpowder. So with a 5lbs cannon ball essentially magically appearing right at the mouth of the barrel (because the ring’s effect), it effectively is a plug plugging up the barrel entirely.