I see this post is a few years old. So now you license is needed to purchase a handgun. (never really was). Never needed it to purchase a part like a barrel. No license is required ever to purchase or carry a long gun in Indiana.
Courts have ruled officers can remove weapons for safety. Probable cause has nothing to do with it. You're thinking of an actual search for contraband or evidence.
He didn't really seize it. The argument is holding onto it for safety the going to return it when the stop is over. I realize your post is several years old and policies have changed. I work in Indy. I've seen this change over the years. I was initially trained to do what you described. Now...