Chokes bored for hevi-shot and other heavier-than-lead (HTL) are not as tight as chokes intended for lead shot. The HTL alloys pattern tighter than lead.

Too much choke will leave large holes in a pattern, just like shooting a choke tube with insufficient constriction. And the HTL shot will be hard on the choke tube (or muzzle).

This is why waterfowlers avoid shooting steel shot through chokes tighter than modified or imp. mod.