hansol - please don't go with a bore size or larger ball. first of all, the larger ball is only useful in an oversize bore, ie: one that measures .735" - some do, or in a rifled bore. A pure lead .735" fired from a .730" smoothbore is an easy way to hurt the gun, maybe blowing the primer. It will definitely raise pressure - a hardened ball, say WW metal is very much worse. A few thousanths smaller is better and use the cup off a wad to centre the ball. The cup will hold the ball in the centre for accurate shooting.

The only way to get away from leading with a bore sized or slightly oversize ball is to lubricate it somehow. Some guys dip them in melted lube and that works. Others use a lubricated wad beneath, but by the time the lubrication gets into the bore, the bore is already picking up lead. Leading destroys accuracy and is sometimes very difficult to remove. Using 0000 steel wool wrapped around a 16bore or 12 bore bronze brush works well. It's the wool that removes the lead, not the bristles. There are easier ways than straight bristle brushes, ie: 0000 steel wool one of the best. The 'wool' won't hurt the bore.

I'd use the fibre wads or - use the Oxyoke felt wads and use a 3/8" punch to cut the centre out of 1/2. 2 wads, the one with the hole on top, ball on top of that - perfect centering. Fibre wad beneath for smokeless loads.

Loading smokeless in a shotgun is similar to loading a handgun or rifle - always start a bit low and work as pressure signs indicate - and slowly. We are dealing with wads and balls not specifically mentioned - possible a different case or primer as well - be cautious and use common sense - don't let over-caution stop you - dropping the charge by 3 or 4 gr. weight of powder & using the lowest pressure loads listed will go a long way towards the rewards of loading your own slug or ball loads.