You may as well use rifle bullets then.

and the rifled bullets will be more aerodynamic and also have rifling for stability. .50 BMG or an autocannon or something.

shotgun slugs aren't usable in any serious, consistent way outside of maybe 20 meters (~60 ft). nasty stuff if you're in range, through.

Bullets do not have rifling, that is done by the barrel of the rifle.

Shotgun slugs can be useful well beyond 20 meters.

https://en.wikipedia.org/wiki/Shotgun_slug#:~:text=A%20slug%....

As a Canadian, I am normally not the one correcting others on the basics of firearms.