From a strictly historical standpoint, what approximate size roundball would have been most commonly used in a .62 cal smoothbore trade gun? Would they have used as big as a .610 for a tighter fit, or would a .600 have been more common, or even smaller sizes to conserve lead perhaps? This taking into consideration the accepted norm of loading bare ball with wadding.
What you are asking about--the difference between ball size and bore size--was called "windage". There were no set standards other than military arms had greater windage than sporting arms and smoothbores had greater windage than rifles.
As
tenngun said, the military objective was to send as much lead down range as possible which meant fast loading and multiple shots. As the fouling built up, they wanted to still be able to load and shoot, so the balls were in the range of 5/100 to 6/100 of an inch smaller than the bore. Sporting smoothbores maybe only need 2 to 3 hundredths of an inch of windage. Rifles needed a tighter ball-patch combination because the patch needed to fill enough of the groove to pick up the rotation and to grip the ball tight enough to impart that rotation to it. I suspect that most period shooters didn't use as tight of ball-patch combination as modern shooters tend to do because there is no evidence they used ball starters, and they probably wanted to be able to quickly load for a follow up shot. In that respect, most rifle shooters probably wanted about 1 hundredth of an inch windage.
These are nominal figures because there were technical and economical limits on their manufacturing tolerances. In addition, smaller barrel manufactures were probably less concerned about tolerances than large manufactures that produced military barrels.
IIRC,
Runewolf1973, you live in Alberta, Canada and may be interested in some information from the Hudson's Bay Company records. S. J. Gooding in
Trade Guns of the Hudson's Bay Company 1670-1970 writes, "High [East India bore] meant that the ball fit the barrel with little windage while those of Low [East India bore] were to be of a diameter in which the ball would roll freely down the barrel."
This is interesting because it shows that the HBC had two standards for windage. It's hard to know why, but possibly some customers used a bare ball with wadding while other customers used a patch ball. Another possibility is that some areas had more consistent ball sizes (such as those supplied by HBC) while other areas had a mix of HBC balls and French balls and needed more windage to accommodate for different ball diameters.
