A violent criminal can hide their gun, except for the minute it takes to use it, then hide it again.
Minute? Dude is a lame draw.
I don't think they always get away with that (especially if it take a whole minute).
All that
is really needed is to make them illegal, and destroy them as found. It's the ubiquity of guns that is the problem.
If all the legal guns were magically gone today, only the bad guys would have guns.
But an oft overlooked dynamic is that criminals tend to dispose of guns after using them for criming.
Eventually they'd start getting caught, and/or the number of illegal guns will decrease down to zero.
But it's too late for even that. Now all ya need for your crime spree are a few shaped pieces of metal and a 3d printer.
3D printed guns are shit, and not a notable threat.
A reasonably skilled amateur with a lathe and a drill-press can make a better gun, far cheaper. It would still be shit, though.
Low quality guns are as big a danger to their user as to their target. A gun is basically a device that causes an explosion in your right hand, and in the case of a long gun, right next to your face.
You seriously don't want anything other than the finest of materials, assembled competently, when using a device that causes an explosion in your dominant hand.
Home-made guns are rare, even where (particularly where) gun laws are strict. Even in the UK, it's not difficult or expensive to obtain an illegal gun, made by a reputable manufacturer (or Beretta).
Criminals in the UK don't eschew guns because the law makes them
hard to get; They eschew guns because the law makes them
undesirable to have.
Having a gun, as a British criminal, makes you much more likely to be caught, and much more likely to face a severe sentence if you are. It's usually easier to commit crimes without them.
If Americans want to reduce gun violence, they need to establish an environment that reduces gun violence. Actually collecting up and destroying all the guns, or making guns hard to obtain illegally, is almost an irrelevance.
As I said earlier, a hidden gun is a harmless gun.
If the merest hint of a gun causes a massive police response, the guns will stay hidden, and the problem is solved.