Scourge of War Boards

There's the load time and misfire rate as well.

Troop quality has a much bigger effect than the weapon though. How a unit performs is almost 100% governed by how good its drill/firearms/manouver factors are over its weapon. I haven't tried it but I suspect an average quality unit with smoothbores could probably beat a poor quality unit with minie rifles in an SoW firefight.

Apart from Headcount (obviously), Experience, Close, Open, Edged, Firearm, Marksmanship and Calisthenics all greatly affect how a unit functions.

If the unit is armed with a smoothbore (model 1842, right?), should I try to close to under 100 yards, or is it just as well to fight it out from 155 or so?

Bringing multiple regiments into a firefight against one opponent is a good option. Also, ground - get higher up and get in cover such as woods, fences, walls or town. You can see how well your men are performing by watching their combat score vs their casualties. If their score is going up faster than their casualty rate, they're winning the firefight. If the opposite is true, you need to do something to reverse that trend.

Pulling out completely from a losing firefight and trying something else is a wise tactic.