Pop-its, one at a time. Then treat. Work yer way up to a handful.

Do the same with the .22. Fun and treats let him know bangs mean goood things.

Graduate from the .22 to something more middle range, with more rounds (9mm, magazine at a time) then, once you are sure he can dig on it, park your truck at the range.

Make your first visit short, with treats again. Eventually park and leave him for an hour or so when the rifles and shottys are goin for broke.

Make sure the sounds and scents always equate to fun and treats as a pup and never worry about it again.