I carry a flexible range rod and a heavy, sectioned, brass cleaning rod (for drawing problem balls), but use my gun's rod for most loading, to build muscle memory (as mine fails).
I've broken a couple of wooden rods - species indeterminate, but probably stained hardware birch dowels - (one twisted off as I tried to free it from a used rifle I'd just gotten) & a used rod, which I'm pretty sure is hickory, (which I got at a trade show barrel because it was the right size & I wanted a spare). The birch sheared along run-out grain, as described before, except the twist off- it just shattered.
The "hickory" had ring marks etched near the butt (which I hadn't noticed until I'd cleaned and polished it.. Early on, I was cautious using it,, half expecting it to break but came to trust it - until loading into an unwiped bore, late in a session. It cracked at the ring. Didn't shear and didn't follow the grain, just fractured at the line.
I used a Delrin range rod until I could get a good (beautifuly stright-grained) blank from Log Cabin.