Now that you mention ICI, Bill - I remember those cans as well. Red with a white oval in the middle with ICI inside the oval, I think in black (might have been red letters).
Seems to me, it was an odd shaped can, with a white plastic cap/spout. For a while, we shot what we could find and it was a menagerie of different brands. I also recall
using C&H with the same loads Lyman used in their Zouave, but in my Hawken. With the powder of the day, that rifle would not shoot well with less than 140gr. 2F GOEX
and a .022" denim patch with a .575", 285gr. round ball. IIRC, I got similar accuracy when using C&H with 165gr. or might have been 170gr. I don't remember the charge
just that it was considerably more than the GOEX or G/O.
My Zouave (also had at that time) needed 120gr. to give good accuracy - same ball and patch, although the rifling was a lot shallower. It gave a solid 2" for 5 shots at 100
yards off the bags.