Does anyone have Kerksis and Dickey's book? I was hoping it might have some details on the rifle canister.

I think I have pieced together a partial answer from Hazlett, Melton and Pawls and some calcs. I've read that both lead and iron were used in various rifled canister.

Melton's site lists a 3" round as having 154 projectiles and something nearly 11 lbs total. Comparing this with his book entry I see a Hotchkiss canister round with about 7" of packed depth and ~2.8" wide internally--but only 7 lb 1 oz. This would hold roughly 154 in 11 tiers of 14 lead smoothbore musket balls (0.65") and a shot weight in the vicinity of 9.1 lbs without the can, lead sabot etc. Hazlett's book references Dickey/Kerksis in saying that 0.69 caliber lead musket balls were used in the 3" Hotchkiss canister. So this all fits except the weight. Therefore the can photographed must have been filled with iron balls.

Iron balls of larger diameter would weigh much less, probably in a 7 per layer pattern 7-9 tiers deep. Depending on size and layer count this would peak at about 6 lbs shot and 2 pounds for sabot/ with 7" of can fill space.