Okay, so here's the deal (sorta, maybe). The Cimarron 16" trappers were different. I don't know if they still are. They have or had a proprietary spring that was very tapered on each end so it would collapse into itself, and a hollowed out end cap which gave you another 1/4" or so. They were supposed to hold ten full size rounds. I have one in 45 Colt. It will hold ten full length (1.58") 45's, but the last round is very hard to load into the tube, and sits crooked on the carrier which prevents the carrier from rising. Some Uberti '73's lack a bevel in the frame's carrier mortice at this point which can cause a jam, but in this case even with the bevel there the jam will happen. The cure is/was to use a knife blade or what have you to straighten that round on the carrier. Then it worked fine. I shot a couple thousand 45 Colts through it that way, but then switched to Schofields just to make it easier to load the tube and eliminate the crooked round issue.
So the answer to your question should be that yes, a 16" trapper from Cimarron will hold ten 44-40's. BUT (the big butt), Uberti didn't always put those proprietary parts in the trappers and suddenly it won't hold ten. And Cimarron almost never had those parts in stock. I think the spec on those guns now says they hold 9, but I don't know if that is to keep people from complaining if theirs don't hold ten, or it holds ten but then jams, or what. I would call Cimarron and ask if the trappers still have those parts so they will hold ten, but I'm not sure if anyone there will know. Ask for Chip, he's been there the longest.