I've always dreamed about opening up a gun store. However, making a go of it seems like it would be VERY difficult. When you consider the high overhead (rent, insurance, etc) and low markup, making it seems heavily dependant on volume and buliding volume takes lots of time and advertising.
You also have to have a fair amount of stock, and the right kind of stock. When you figure in what even a minimal stock would run, say 100 guns, several thousand rounds of various ammo, cases, tools, and general stock your looking at a very large investment. The only gun shops that I know of that really make anything are the large, well established ones that have been in business for years and have a loyal customer base. Speaking of stock, you have to have what people in your area want at the time. I don't even want to think of how many shops are sitting on a stock of hunting rifles they can't sell thanks to Obamania and the frenzy for EBR's.
I know a lot of people that run their FFL out of their home as a part time/retriree business and use their small profits to bankroll their hobby. They usually only have a minimal stock (if any) and make their money doing transfers and special orders. Most of them have the luxury of seemingly knowing everyone, and get most or all of their business by word of mouth.