If nothing else, I've found that if I walk up to an employee who's BS'ing with someone and stand there patiently, obviously waiting for some attention, that usually works.
You also have to consider how many people a gunshop gets every day that want to see this or fondle that, or ask this or argue that, or blah this or blah that, and then walk away without buying anything. I'm sure they get tired of tire-kickers, and if they don't know you personally, how can they tell if you're a buyer or a just another yahoo? If they hear you say "I need...", that means you're serious and worth the time.
Just about the same way in most any kind of place of business.