1. The cowboy, however, seldom used such a contrivance but did his gentling in the middle of a bare coral or wherever he happened to be.

Ans: The cowboy, however, seldom used such a contrivance but did his gentling in the middle of a bare corral or wherever he happened to be.

1) no comma before but because "used" and "did" are compuond verbs

2) the place where horses are kept is called a corral.