What ammo can I use in my shotgun?

The 20 gauge, using standard slugs, such as a foster style, will prove an effective weapon for feral hog hunting as long as you are mind full of it's limitations, If I remember correctly, the Hawthorne merely has a bead sight and is mainly used for birds. Under this scenario, your effective range will be 50 yards or less. The slug can travel the 200 yards, but it would take an exceptional marksman with considerable experience with that specific weapon to precisely place the projectile into the kill zone of a pig at >75 yards.