Gun show loophole
The gun show loophole is a lie perpetuated by the liars for the ignorant. Most of the sellers at gun shows are Federal Firearms Licensees (FFLs). By law, they're required to perform background checks on all sales, regardless of where the sale takes place (either at a gun show or at their brick and mortar store). The loophole is that in theory, two parties can meet at the show, and make a deal to go to the parking lot and make a sale (trade). However, that is against the rules of all the gun shows I've been at. And that can happen anywhere -- online, at a gun store or range, or at a McDonald's. Even there, if the seller believes the buyer is prohibited to buy, or is on any kind of controlled substance, the sale is actually deemed illegal. So the imaginary "loophole" is that it is not a crime to sell or give a gun to someone else who has a legal right to have it, without the government involved?!
BTW: no mass shooter and few criminals have ever gotten a gun this way. Think about it, if you're a criminal, do you want to be going up to strangers and saying, "Hey, I want to buy that gun". It's easier for them to get it legally, straw purchase (illegally), or through more shady and thus less traceable characters. If the left had found someone that had used this to cause mayhem, they would have televised the crap out of it -- and they never have.
What they want to do is outlaw ALL private party transfers, under the false flag of it a loophole for you to be able to loan a gun to a family member, or sell a gun to a friend, without government being able to track it. And that's not going to happen. Gun owners would file off serial numbers, and you'd create a burgeoning black market if the government tried. Then what? You're going to ruin people's lives for not believing that government should be able to violate your 1st, 3rd, 4th, 5th amendment rights to privacy -- all as a way to infringe on your 2nd amendment rights as well?