The heavier the lead load the more internal pressure, assuming the same amount of powder. With less powder and more lead, hmmmm, hard to say. So the 1oz loads might cycle, might...
One thing you might also do is take a dremal and some very very fine polishing compound and polish all of the moving parts. Then very lightly oil with a teflon contianing oil.
Can you take the shotgun down to the point you see the "ports" drilled in the barrel? Are the clear, any lead deposits shrinking the holes size and capacity? And the gas ports and pistons clear of all the old soot and such? You might want to soak the internal pasages in solvent and blow clear with brake cleaner or compressed air to get them clear.
I don't have any experience working on semi shotguns, just rifles and pistols, but hopefully I was able to help.
later,
scruffy