I imagine that the momentum would be conserved. So if the rifle normally shot a 30 gram ball at 300 meters per second, it would shoot a 5 kilogram ball at around 23 meters per second.
The larger size and lower speed of the cannon ball would likely reduce the range.
The larger size of the projectile would spread out the impact causing reduced damage.
The ballistics would be significantly different making it far harder to hit with.
This is how I would do it in my game:
Reduce the damage from 1d12 to 1d10
Change piercing type to bludgeoning
Reduce range from 40/120 to something like 20/60
Add knockback of 5 ft to medium targets or 10 for small
The really neat thing would be shooting non standard rounds that wouldn’t be possible from a musket like incendiary or smoke rounds.
I imagine that the momentum would be conserved. So if the rifle normally shot a 30 gram ball at 300 meters per second, it would shoot a 5 kilogram ball at around 23 meters per second.
This is how I would do it in my game:
The really neat thing would be shooting non standard rounds that wouldn’t be possible from a musket like incendiary or smoke rounds.