I have built many Flintlock smooth bores and hunted with many of them. They are a hoot and accurate.
When using flintlock smooth bore load with the "VM Star method"... two Hard cards over the powder and one card over the shot !
Never use a Fiber wad ( that is for modern guns) with flintlock ignition it is too slow of a delay!

A good 18th Century rule : More powder less lead - shoots close more spread! Less powder more lead shoots far kills dead