My old 1100 with 22" iron sight/fixed IC will hold 4 to 6 inch 5 shot groups @100 yards with WW 1oz. rifled slugs (aka. lead thimbles).
Accuracy begins to drop off after 15 rounds or so, from lead build up.
I de-lead the bore with 4 ought steel wool wrapped around a 10 gauge bore brush and spun with an electric drill - do this outside with the barrel downwind of you.
Note: If you have a choke tube barrel - do not use the spinning bore brush at the interior junction of the bore and choke tube!
The smoother the barrel interior becomes the less lead buildup occurs. YMMV