Opening a gun shop requires a Federal Firearms License or FFL, which can be difficult to acquire. Besides selling guns, you can expand your inventory to selling knives, classic arms and other items that fall into the firearms category.
Acquire a FFL from the federal government. There are lots of rules involved in applying and being approved for your FFL. FFL applicants must pass all scrutiny or they will not receive the license. To get your FFL you must be at least 21 years old. You must not be prohibited from buying or selling guns and ammunition. If you violated any Gun Control Act regulations, you will not get a license. You FFL will be denied or rescinded if you are caught in a lie on your application. Before receiving your license, you must establish a location to buy and sell your guns. If you plan to open more than one gun shop, each must have its own FFL license
Find a good location to open your gun shop. You have to have this before you can officially open the shop, but don't make a major financial commitment before you are fairly sure you will get your FFL. Once you do, you must inform the local police of your gun shop opening. You have to get local and sometimes state approval for a gun shop location.
Keep a "bound book" which holds all your transactions of gun sales to individuals. It must be kept on the gun shop premises at all times and the pages have to be numbered consecutively in case of an audit.
Install gun safes for at night and glass cabinets for during the day. The law requires you to store the guns in a place that is not easily accessible. This minimizes the chance of the firearms being stolen.