I should do a double-feature review of Rio Bravo and El Dorado since El Dorado was a virtual remake of Rio Bravo. In Rio Bravo, you had a young gunslinger named Colorado...in El Dorado you had James Caan playing a young guy (who couldn't be worse with a gun) whose name is that of a different state, Mississippi. And, if you can believe it, we had Ed Asner playing the bad guy...
Achim, yes, you got the plotline right. Caan can't hit the proverbial broad side of a barn so they give him some kind of a scattergun if not exactly a shotgun. It packs quite a kick. When he uses it in a fight it illicits one of my favorite lines..."Well, he was limping when he left," says Mississippi to which John Wayne's character retorts "He was limpin' when he got here!"