I read recently that was describing a cavalry, full of "horses champing on their bits, eager to rush forwards into the fray." I have always known it as "chomping". Is "champing" a typo? Is "chomping" or "champing" correct?
Chomping is the typo, according to M-W:
I grew up around horses and mostly heard "chomp", though.
NGram usage shows that "champing at the bit" is the most common form of the phrase followed by "chomping at the bit":
Options 3-5 are significantly less common.
That being said, other sources contest this and note that "chomping" is much more common:
There is no doubt, however, that "champing at the bit" is the original idiom and "chomping" is simply replacing "champ" with the more modern "chomp". If you want to be technically correct, use "champ" but virtually any native English speaker will understand your intent regardless of which variant you choose.