Pete!
As Editor of the Padre's delightful book(s), I believe I can provide some answers, but if you don't like them, do what you prefer!
Regarding the two different means of adjudicating Artillery fire effects, I have only used spring loaded cannon and matchsticks. However, until you have some of these in your arsenal, the tables will do.
And, "Turns of Fire" is meant to provide the total number of Game Turns that weapon can fire before running out of ammunition, NOT how many times it may fire in the same turn.
Note, while many games are decided before anyone is reduced to hearing only unsettling "clicks" from their empty weapons, this is part of the value of providing Supply Wagons and a Logistical Staff to make sure no one ever has to.
And please accept the invitation to join the Official FLW Yahoo! Group moderated by the Padre himself where you can ask any questions you wish, as well as read of new rules ideas, game variants, battle reports, information on acquiring figures--and shooting guns!--historical info, and so very much more by as Gentlemanly a group as ever you'll find on the Internet.
Just remember, ties (School or Regimental) must always be worn in the mess, and to name your first post to the group, "Stranger In The Mess!," so everyone will know to come and welcome you.
Play on, MacDuff!
TVAG