Generally speaking here you will most often get the best accuracy/grouping from improved cylinder or cylinder (no choke) barrels, but not always.
every shotgun/barrel/ammo/choke combination is a law unto itself. Case in point...My Maverick 88 shoots the PMC brand slugs the best; almost worthless with Rem "Sluggers", while Shooting Budds Maverick 88 prefers "Sluggers" over any other brand.
Buy a small box of as many brands that you can find, and blaze away. One or 2 brands will be the best, and some brand(s) you could do better by pulling the slug out of the shell and launching it with a "Wrist Rocket" slingshot.
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