ONLY with regards to gun shows. Purchasing from a brick and mortar FFL dealer is a TOTALLY different matter. Also if you purchase a firearm online, it still has to be shipped to an FFL, so there's no loophole there. On the contrary, in Canada, you can have the firearm shipped to your local post office.
With regards to gun shows, a criminal needs to keep track of when and when shows are going on, get to the show, and then find a seller that will just hand a firearm over to them for cash and not require any paperwork (which I've never seen take place at any gun show I've ever been too. Trust me, I've been to a number and in several states. Most gun owners are suspicious as hell due to perpetually getting an undeserved bad rap in the media). Also, most mass shooters have utilized LEGALLY acquired firearms (https://www.kunc.org/post/1982-74-percent-mass-shooters-obtained-their-guns-legally#stream/0). The criminals who blow away folks here in Baltimore, aren't hindered in the slightest by our tough firearms legislation. The only folks who are hindered are the law-abiding folks who have to fill out yet another form, go through more training, go through more background checks, get fingerprinted AGAIN, etc., etc. Criminals naturally don't worry about any of that stuff, get the guns from their contacts on the street, and keep blowing folks away.
The hard reality is more laws do not necessarily equal saved lives. Criminals will kill and maim with anything and everything. That said, I'm down with training, licensing, background checks, and with prohibiting certain firearms from being carried in the street. Just once I've gone through all those checks, let me live my life and protect myself, loved ones, and property. But folks won't do that. They don't leave folks such as myself alone. They keep saying things like more checks, ban this, ban that, even the 2nd Amendment for that matter. That's the point: NO law will EVER be good enough for the folks that are scared and don't like guns. And for all the talk about distrusting the government and how corrupt it is, I am BOGGLED by the fact that so many folks are so willing to trust the government to fix the problem of gun violence.