Goose, A few years back I got interested in smoothies and it turned into an education with quite a few surprises. First off, I learned that the stories about smoothbores not being accurate are just plain bunk. Once a preferred load is worked up the old smoothie will give a lot of rifles a run for their money. The stories about poor accuracy came from military muskets where speed in loading and the ability to fire shot after shot without swabbing the bore was the goal. Balls used were substantially smaller than bore size to accomplish this and accuracy, or lack thereof, was a secondary consideration.
Another surprise for me was that using a cloth patch didn't necessary result in the best accuracy. Shotgun wads, and by that I mean a ball sandwiched between over-powder and over-shot card wads, often did as well or better on the target than a tight patch. Using wads also had another advantage, I could shoot a single ball, buckshot, or birdshot with the same wads.
A really big surprise came when I tried tow. I frankly didn't expect much but it was historically correct so I gave it a go. I dumped down a powder charge, stuffed a wad of tow in the muzzle, pushed a ball down on it and added another wad of tow. The whole shebang was then rammed down to sit on the powder. I'm guessing that the rear wad tended to get blown forward to surround the ball and center it in the bore. Whatever happened, the result on the target was good and once again I could shoot single ball, buckshot, or birdshot.
Unfortunately, I have never owned a .69 cal smoothie. I've had Brown Bess in .72 cal and other smoothies in .62 cal/20 gauge. and in every case I used a ball that was a few thousandths smaller that actual bore size. For instance, most of the .62's would actually mic between .615" - .618". I used balls that measured .600" - .615" with good results. Check with Track of the Wolf or one of the other outfits to see what they offer. Better yet, Jeff Tanner over in England will custom cut you a mould to your specifications and his prices are reasonable.
Have fun,
John