’m glad you asked this question. You should not shoot slugs—or any other shot—through your barrel without a choke in place, since there is a very real possibility that you will damage the threading. I assume that you’ll be shooting a Foster-style slug—one that has rifling. The conventional wisdom has long been that these slugs perform best with an Improved Cylinder choke. Though ammunition is highly variable, and all guns digest ammunition a little differently than one another, I’d be inclined to start with an IC choke. If your accuracy with this choke is acceptable, stick with it. If it doesn’t, experiment with other chokes until you find the one that performs best. Regards, Ken Bailey
https://www.outdoorcanada.ca/what-choke-should-i-use-when-shooting-slugs/
none/no choke would be ideal with a slug.