Depends on your technique and quality of your rod, hanshi. .009" per side is about perfect, good accuracy and a good seal.
I load .682" pure lead ball with .030" (12 ounce denim) patches in my .69 - even tried the .036" (14 ounce denim) & loaded them with the hickory rod. The thicker ones are WAY over the top,
compression in the groove bottoms-wise. Smack in down inside the muzzle with the short starter and now, except for the longer bearing surface, they are groove diameter. 9/16" to 3/8" rod.
.690 + .024 = .714"
.682 + .060 = .742" - .028" comp. = .014" comp. each side - these are about perfect and are VERY accurate.
.682 + .072 = .754" - .040" comp. = .020" comp. each side - these are a bit tighter than is comfortable loading.
Even the .030" patch is VERY difficult loading if not using very soft lead.
For WW alloys or harder, I use a 15 bore ball, .677", currently, with the 14 ounce denim which I measure at .036", thus the ball + patch is .677" + .072 = .749. The total compression is ..035 divided by 2 = .0175 per side, which works for a non-freezing hunting load. Freezing weather means paper ctgs. with .682" balls.
I should note, the 15 bore balls, whether pure or hard alloys also shoot well with 12 ounce, or .030" denim.
A friend gave me 3 yards of 14 ounce, so that is what I am using.