It's my policy to not get involved in armchair-murderer discussions
That is fine, though I must remind you that policemen and other figures in that field do exactly that on a regular basis. It's also one of the better ways to implement effective legislation against crime rather than creating some kind of loop-hole ridden mess, created in a hurry based primarily on emotion.
I'd rather criminals have "a thing that looks dangerous but is not capable of shooting people" than "a thing that looks dangerous and which is capable of shooting people".
Regardless of what you would "rather", criminals will get their hands on a live firearm if they know how to get it. It would also be completely off the radar. You'd have to be a very silly criminal to murder someone with the same gun the police have allowed you to use and keep records on.
Owlbread, the problem in the US is that they DO often shoot people.
I agree. There are cultural differences between the UK and the USA that mean our criminals are apparently less trigger happy. That does change things a fair bit.
There are also cultural differences between the Czech Republic, a country with possibly the most liberal gun laws in Europe, and the USA. Though they have extremely liberal gun laws, their annual firearms-related deaths are a predictable 800 or so. The USA on the other hand has literally thousands of deaths per year from handguns alone. I understand that there are enormous population differences, but it's still striking nevertheless. The Czech people apparently have more liberal gun laws than most American states.