I was taught to do it that way by my dad when I was a pup. Been killing adult quail that way for 40+ years. Fast and easy but I suppose doing it so often makes it become second nature.
But hey, what do I know. Just a dumb ol farmer. LOL
Shoulda made it clear that was for OP, not you. It's not uncommon to hesitate with a new method and injure the animal instead of kill it—I've seen people do that to frailer animals than quail. Trying to avoid some heartache.