I think you're on to something, Rich!
I would think that the concentric growth rings of a sapling might give the stick more strength and resistance to lateral stress, as compared to a rod sawn or riven from a larger billet, even if the grain of the split or sawn rod is straight.
The rod that is shown with this old trade gun, which was collected from the Assiniboine at Fort Peck, was definitely made from a sapling:
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That musket is in the National Museum of the American Indian, catalog #20/1459. Here is a link to the museum's web page which shows this gun and rod, and several more photographs:
Flintlock Trade Musket
You can tell from the slight "waviness" of the rod, as well as the little knots, that it was made from a sapling. That second photo shows the tapered tip with the wire-coil worm or wiper more or less permanently attached. In the first photo, you can see how the other end of the rod has been carved to make a jag. I don't know what kind of wood it is, but I believe it could very well be choke cherry.
I'm inclined to believe that improvising a ramrod from a sapling must have been a pretty common practice. James Fenimore Cooper's "Leatherstocking" commented on this in
The Pioneers:
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I cut a persimmon stick sometime last year, intending to try a sapling rod in my own Northwest gun. Ash is pretty scarce where I live, and I didn't find a suitable hickory sapling. There is plenty of cherry, though, and I'm interested in how your cherry rod performs for you. Persimmon is in the same family as ebony, so it should make a tough rod. It has a couple of curvy spots that will need to be straightened, though. We'll see how that goes.
Thanks for posting, and for telling about your project!
Notchy Bob