Throwing a shrunken cannonball would work the same as shooting it out of a gun. If you throw an object that weighs one ounce at the time, it flies away with the amount of energy it took to accelerate an object that size to whatever velocity you give it. When the shrinkage magic stops, its mass returns to normal. This doesn’t change the amount of momentum the barbarian or the flintlock gave it. Think of it this way - if you get magically shrunk and you pick a flower, when the magic stops and you grow back to normal size the flower doesn’t also grow. It wasn’t affected by the magic and isn’t affected by the magic going away. Neither is anything else you acquire while shrunk, like momentum.
I noticed I didn’t even finish my previous comment, oops.
I do understand the physics, I work in engineering. I also looked at the spell desctiption from 5e D&D, it reduces the weight by 8, so the reduced weight would still be about 1-2kg. Not exactly a bullet yet.
Throwing a shrunken cannonball would work the same as shooting it out of a gun. If you throw an object that weighs one ounce at the time, it flies away with the amount of energy it took to accelerate an object that size to whatever velocity you give it. When the shrinkage magic stops, its mass returns to normal. This doesn’t change the amount of momentum the barbarian or the flintlock gave it. Think of it this way - if you get magically shrunk and you pick a flower, when the magic stops and you grow back to normal size the flower doesn’t also grow. It wasn’t affected by the magic and isn’t affected by the magic going away. Neither is anything else you acquire while shrunk, like momentum.
I noticed I didn’t even finish my previous comment, oops.
I do understand the physics, I work in engineering. I also looked at the spell desctiption from 5e D&D, it reduces the weight by 8, so the reduced weight would still be about 1-2kg. Not exactly a bullet yet.