Before I do, I want to go ahead and make some general comments that have been percolating about as I've cycle to and from work and taken the baby out on her evening pram ramble.
For a start let me say that I know very little about the performance of the small arms and field artillery of the American Civil War. I chose this period as much from a desire to learn about it as I did to resurect Charles Grant Seniors' ACW rules. That being said, I am trying to fill the gaps in my knowlege as fast as I can. The internet has been very useful to me on tactics and though I blush a little to say it, the weapon data in Airfix Magazine Guide #24, American Civil War Wargaming by Terence Wise. I know, I really ought to be reading Paddy Griffiths, but I can't afford him at the moment and TW is at hand!
My understanding of the basics of the period was that rifled muskets and breech-loading rifles had sufficient range and accuracy to make serving smooth bore (SB) and the newer Breach Loading (BL)artillery sufficiently dangerous that it could no longer be used offensively - that is it could not be prolonged forward to support infantry attacks. BL artillery could play on attackng infantry at a distance from which they could not easily reply, while the cannister discharges of the SB guns made them quite formidable defensive weapons still. These with entrenched infantry who were using more accurate and faster-firing long-arms meant the defensive was the stronger tactical means and accounts in large part for the huge casualties sufferd by both sides.
It is currently my belief that the war began with smooth-bore percussion cap muskets being the most common infantry small-arm with rifled percussion muskets and then breech-loading rifles superceeding them as the Civil War progressed.
Looking at some of the more common weapons of the war, we see that the standard weapon in the early months of the War was the M1842 percussion, muzzle-loading smooth-bore. This weapon had an effective range of 150yds and a battle-field range of 75yds. The most common weapon on both sides (so Mr Wise says!) was the M1861 Springfield Muzzle-loading rifle. It had an effective and a battle range of 500 and 250yds respectively. The performance of the Enfield and Remington muzzle-loading rifles was comparable. All weapons had similar rates of fire to the M1842 of 3 rounds per minute. The Sharps and Henry Breech loading rifles has similar ranges to the Remington M1862 of 600yds effective and 350 "battle", but vastly superior rates of fire; 16 and 20 rounds per minute respectively.
Turning now to the most common field artillery of the period we can see why the Guns were forced onto the defensive. The following are maximum effective ranges:
Shell: Min - 250yds Max - 800yds
Shell: Min - 250yds Max - 900yds
12PR RBL Whitworth
Shell: Min - na Max - na
3" RBL Rodman
Shell: Min - 250yds Max - 1400yds
20PR Parrott Rifle
Shell: Min - 250yds Max - 1400yds
I could continue, but I think that really the artillery (especially the SB types) was in a tough spot supporting attacks with the classic blast of cannister to soften things up! Shell couldn't help at rifle battle ranges, and shot couldn't blow huge holes in the more dispersed infantry formations of the time. They could do considerable execution upon charging infantry however.
Now, looking at the Grant Rules with this in mind, I have decided to adopt the Grant 10yds to the inch ground-scale.
Knowing little about ranges other than that the "musketry" range is 18", what must we deduce? 18" translates to 180yds which is close enough to the 150yd range of the M1842 percussion musket for me to assume that this is what Grant may have had in mind.
The 60"\600yd range he gives SB artillery in "The War Game" is obviously quite conservative, but I could swallow this as an effective range for unsighted SB artillery. Likewise I can but the 24"/240yd cannister range sufficiently to import the rules complete into the ACW rules.
This begs the question though, did Grant bother with additional rules to handle rifled weapons? Part of me thinks he may have; he always seemed on a quest for realism in all his writings. Another part is discouraged from this view when I think of what material may actually have been available to him in the late 1950s! this is even more the case for Featherstones' Horse and Musket rules which claim to be able to be used up to the Franco-Prussan War yet which apart from a mitraieuse rule seem terribly generic.
I am inclining to the belief that Grant probably had no reliable or complete information on the rifled weapons of the ACW and that he probably ignore them. If this is so, I might be able to look at importing the Musketry and artillery rules directly from The War Game. The only thing stopping me at the time of writing is a small comment that CS Grant makes in the War Game Companion on the transition of the ACW Rules to those of The War Game:
"The rules were new but a number of the mechanisms had been established. at least to some extent, during our American Civil War Games. Of course the style of warfare was different and that meant serious changes. The rules for movement and manoeuvering of troops needed to reflect the ratherstylised and rigid formations of the mid-eighteenth century. The use of cavalry as shock troops rather tha as mounted infantry needed to be catered for. Both artillery and musketry would be seriously less effective one hundred years earlier than they were in the American Civil War, and then there was the issue of morale..."More information might be necessary!