This being done, I was re-reading the Grant Artillery rules and I came across this passage on page 70 in the chapter on Canister:
"... the Canister Cone. It is patently not a true cone, but the name reflects the original shape and is used for the very simple reason that I cannot think of another."Furthermore, on pp 68-9, Grant states:
"For long in wargaming the general assumption seems to have been that the firing of canister produced a shot pattern similar to a kind of elongated cone... wargamers who, like myself, preferred to have an actual device to indicate the pattern and casualties of canister fire in their games."It may well be that at the time he was using a canister cone for the ACW games, Grant may not have been using the familiar canister cone at all. Rather he may have been using something like an elongated equilateral triangle. I do not know it's dimensions, but would guess that it would be 28" long, with internal sub-divisions at the 6.5" and 14" points along from it's apex to define the increasing lethality of canister as you approached the muzzle-end of the gun.
I'd guess 28" as Grant has canister range as about 240' which translates to about 28" at his 1"=25' ground-scale. The smaller sub-divisions are guess-work based on those of Grants' polygonal canister cone.