The use of guns is, of course, a standard of certain genres, and many a trope has been dedicated to analyzing their use and the various Stock Phrases that they bring. In this case, you have two characters: one is an experienced marksman, and one is inexperienced. At some point in the story, the need for the inexperienced individual to use a gun comes along. Sometimes the training takes place on a simplified Shooting Gallery, perhaps during a montage of some type. It may also work as a moment for the relationship between the two characters to be showcased: sometimes as parent and offspring, sometimes as mentor and student.