I'm at the point where I'm not sure if you're trolling or just stubborn and stupid.
In state or out of state including online sales, when purchasing a firearm you must do it through a licensed retailer or business, unless it's a private transaction such as gun shows. That loophole is actually on its way to being plugged.
All firearms require background checks, not just handguns. The only exception to this rule is black powder, which is no longer considered a firearm to the federal government.