John Bidwell talked to anyone who had knowledge of travel in Indian Territory. One of the things he needed to know was what kind of gun to take. There was no more important piece of equipment than a gun.

“My gun was an old flint-lock rifle, but a good one. Old hunters told me to have nothing to do with cap or percussion locks, that they were unreliable, and that if I got my caps or percussion wet I could not shoot, while if I lost my flint I could pick up another on the plains.” (Echoes of the Past, p. 113)

Rifles with percussion caps were the modern gun of the day, but there were still plenty of flintlocks in use. A flintlock rifle fires by by scraping a bit of flint rock down a steel plate  which makes sparks that fall into a shallow depression filled with gunpowder. When the powder in the pan is ignited, it ignites the powder in the barrel, which propels the bullet. A flintlock may have been more primitive than a percussion cap rifle, but it was going to be more reliable where John Bidwell was going.

How Stuff Works has a good description of how a flintlock fires, with this diagram.