A little large for my girlish hands. Still, I found a good quantity of slingshot-sixed pebbles...and I have a slingshot today, but marbles are my ammo. ;o]
Marbles work well too, but when you're a kid and you have to BUY them, you don't use them for ammo!
Fortunately, where I grew up we had a secondary source for when the Buckeyes weren't falling at our feet off the trees. The railroad cut through the west side of town and if you walked the roadbed (ok, I know, that's trespassing - but back then no one was thinking about blowing up a train so no one hassled us...) you could find all sorts of stuff that bounced out of the cars. If it bounced out of northbound cars it was usually coal heading to the Lake Erie docks. If it bounced out of southbound cars it was those beautiful round taconite pellets...
Thus Mother Nature and the Chesapeake & Ohio were our main suppliers of slingshot ammo!