Suppose the end of the world came as we know it, and you only had one weapon. The Midland Back or similar single barrel shot gun with a 18" barrel.k in 12 ga. You were given two 8" inserts, the 22. cal and the 9mm. And the choice of picking one more insert. Which would you choose. Please this is not to compare other shotguns, pistols etc. Do not consider reloading as a option This is not to rate the gun. Just your caliber pick. By the way here is a target I shot when new at 25 yards with a 9mm insert. The shotgun only has a bead site and a small grove in the rear. I have no doubt that 90% could do better than I could with this setup. But will give you a idea of what it is capable of when New and not much practice. *These are rifled inserts .