Col. Batguano said:
Why again do we use no patches in cannons, resulting in windage around the ball?
Yes pressure reduction upon firing is one benefit.
The other is to make loading easier.
Recall the increased resistance to load a patched ball in even a smoothbore over the resistance of loading an unpatched ball in say a .50 cal musket for instance. The resistance is from friction of the circumference of the ball against the wall of the barrel.
A .50 cal ball has a circumference of roughly 1.6 inches. So you have 1.6 inches of surface area in friction contact with the barrel wall to over come.
It is recommended the over 1 inch cannons not be patched. My little 1/6 scale 42PDR 1841 boat howitzer has a 1 inch bore. The circumference of the 1 inch ball is 3.14 inches. That is lot more surface area in contact with the bore and a great deal more friction to overcome.
I also have a golf ball bore 1/5 scale of an 8 inch siege howitzer. Bore 1.72 and 5.72 inch circumference-surface area to overcome friction.
Now add in the other factors that were present during war shooting when cannons were deployed. Round shot was iron-it rusted, it wasn't always perfectly round. Windage was needed to get this shot down the the bore. Under normal circumstances shot was gauged before use, but this wasn't always possible in the field and during the heat of battle. There of course was the other issue that we don't have, that of an improperly or poorly cleaned fouled barrel. When a company of troops with fixed bayonets is charging your position you might cut corner loading.
Of course in our case we have plenty of time to practice safe load procedures insuring we only use the correct and perfect projectiles in immaculately clean bore---Right? Right!
I can tell you from my own experience loading 1 inch round
lead balls, that it is very easy to stick ball in a bore. Several year ago while loading I slightly missed the bore and banged a ball against the muzzle, oops. Repositioned the ball and loaded the ball properly only to have it stick halfway down the bore. What a nightmare. That little tiny ding was enough to jam that ball.
I have gone so far now as to not even use lead balls in my cannons. I use nothing but zinc.