Sounds like my old standby "movie that nobody's ever heard of:" Dance of the Dwarfs/Jungle Heat
The scene wherein Jimbo ("Harry Bediker") played Russian Roulette ("Cuban Roulette") sounds almost exactly like it, and the helicopter and muck monsters rising from the swamp (one of the titular "Dwarves") only makes me all the more sure. Was there a second bandit who ran off and eventually fell into a boiling pit of mud?
Does this look like it?: