In my recently published book I discussed how increasing gun control legislation is likely to create a market for firearms produced by organized crime.
Today I came across this interesting blog on improvised and home-made firearms across the world. Notable is that while some examples are quite crude, some are very sophisticated and seem effective for their purpose. Many of these guns are produced in countries with very restrictive gun laws such as Australia, China and Northern Ireland. This photo shows an SMG factory that was in business for 20 years in Northern Ireland.
This weapon was produced in Denmark right under the noses of the Nazis: