Smokey,
On the plains, a shorter barrel was more convenient for horseback.
Up here and I'm sure down there as well, we see scrapers made from maybe 6 or 8" of gun barrels.
Quite often they were cut down shorter than 30" for buffalo running. I've seen them down to maybe 20 inches or so.
We do see some "reservation guns" and these we are told were cut down to hide under a blanket, but they may simply be buffalo running guns never handed in.
30" is fine for a trade gun on the prairies, and if you do buffalo running, you can make a 6-8" hide scraper and Still be OK!
No sense to a wee short effort in a canoe, and no provenance either as far as I can tell.
PS,
A short flint buffalo gun was found on the prairie east of here a few years back. (Flint trade gun) wood very checked, but still sound. Had a maybe 20 or 22" barrel. Sometimes they were lost in a buffalo run, and never recovered.