I like the concept of Betting before the duel start,really nice idea :D If you can spin the gameplay more it would be perfect, relying alone on Dice kinda kill the vibes of a Cowboy duel.
I made a game similar before without the Betting, about cowboy dueling Quickdraw, then aim. while aiming, time slows down making it intense because you only have one chance or you dead. thats why i really like that betting Idea you have here :D