Earlier quoted context omitted.
Not true. Even here in the UK I can walk into an antique shop and buy a gun that can be put back into service in minutes. Guns aren't, and never have been, the thing that you need to regulate to keep down gun crime. Bullets are. If you have a gun, you have a gun for life. But if you don't have a never-ending supply of bullets, you might as well have a paperweight. Bullets are harder to get and harder to make than gun…
You're going to rob a store with a flintlock pistol? With a 3d printed gun you can. Furthermore, bullets are much harder to regulate than guns. Plenty of people have access to bullets and can make 50 of them disappear, claiming they shot them. "But if you don't have a never-ending supply of bullets," Why a never-ending supply? You only need 5 bullets at most for each robbery or murder you commit. A box of 50 can last…
Can you?
The reason guns work so well for robbing is because they work really well at threatening. This is why you can rob a store with an airsoft gun or with children's toys with the orange bit removed. Toys that look like guns work great, but guns that look like toys? Not so much
The fact that it seems incredibly unlikely that they will become more than single-shot anytime soon basically means that even firing the gun during the robbery isn't going to be a very good way to rob a store.
The best you could manage is to fire your single round into the ceiling to demonstrate that what you had was a gun, and then hope the clerk doesn't realize that you can't fire any more shots. Meanwhile if you do that then you have just blown any chance at your robbery being uneventful and unnoticed.
You would honestly have better luck trying to rob a store with a jacket and your index finger. Considering the availability of jackets and index fingers, you would have to be a complete idiot to choose the printed gun instead of your index finger.