Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
1970's Trucker Movies. There's a forgotten sub genre that should probaby stay that way along with CB terms like "hogging the zipper," "bears in the air," and "double nickles on the dime." In this fine example of the genre, the hero, an independent trucker, is at war with corporate thugs who have already tried stopping him with beatings, blacklists, murder indictments truck attacks and crooked cops. Those don't work, so they try a new tactic. He goes home and finds his truck trashed and covered with spray paint. When he opens the cab he finds a rattlesnake inside, put there to kill him, of course. He uses his shotgun barrel to lift the snake out of the truck then throws it on the ground and shoots it with the shotgun.
They used a live Western Diamond-backed Rattlesnake, which is appropriate for the Tucson setting. We don't see if he actually shot the snake, but that's unlikely.