Eric,

I don't see any way he would have been firing canister at long range. Case shot would have been the appropriate ammunition for antipersonnel at that range.

If it helps I've noticed some references to artillery on the web (primarily from Europe) that refer to ACW era canister as a type of case shot (or the reverse--I can't remember which.) That has puzzled me and I've not tried to resolve that grouping. Functionally case is trying to accomplish the same as canister, but at long range--behaving like canister in the last 50-75 yards or so when the fuse timing is right. So the captain could have been using some ambiguous period nomenclature.

If you've got battle field finds and ammo reports that support your interpretation, and it fits with common sense artillery tactics, then it doesn't make sense to get hung up on a single word. Simple explanations that explain all the evidence are usually best. Does he mention fuses or bursts or anything else that would obviously preclude canister at the open?

Shawn