Well, the simple answer to the question is...you can shoot slugs through it! But without more information it is hard to make more meaningful suggestions. Does the current barrel have rifle type sights...or just a bead? Is it a " rifled" barrel...or a smoothbore? Is it equipped with any type of interchangeable choke system? All of these questions, (and their answers), will have an impact of what will work best.

When my son was preparing to hunt whitetail on Aberdeen Proving Ground (late 1980' s) it was limited to shotguns with slugs, or muzzleloaders. Not only was he young (about 9 or 10) but he also had muscular dystrophy. I bought a smoothbore single shot in 20 gauge for him, with rifle sights. (Rifled barrels were not nearly as common then!) We folded over the rear " open" sight and I had a " peep" sight installed on the rear. (It was a Williams Fool Proof.) I unscrewed the smaller aperture, stored it, and then we sighted in the " larger screw hole" . Much like a " Ghost Ring" before they were manufactured and called that. We also had the stock shortened by about 1 1/2" and reinstalled the recoil pad, (to fit the gun to him). We used Brenneke slugs which were very accurate to 75 yards. (Pie plate accuracy.) The Brenneke' s were heavier and more effective than other Foster style slugs for the 20. (But with an increase in recoil....and in retrospect I should have had my son use the lighter slugs in lieu of his condition.) The military base required a " qualification" with your gun...and my son qualified...but he took a beating from the recoil of those 7/8 ounce slugs. (He was already weakening from the disease by then.)

But to make a long story short....really need more info to provide information that will be worth much to you!