I do pretty much the same as Mite. Except I start with a .22 blank pistol. Fire when they flush, tends to simulate what will really happen when hunting, plus his/her attention is on that bird flying away. I don't have a .410, so I then graduate to a 20 gauge and then 12. Also, get the dog accustumed to being around the shotgun first. Work the action alot around him/her and lay it next to their kennel for a little bit each day.