Operating out of his garage Paul Edmunds, 66, imported huge quantities of antique guns from the US.
But while 17 pistols criminally-linked to Edmunds have been taken out of circulation, police said of the 280 guns imported between 2009 and 2015, the whereabouts of 207 remain a mystery.
The "firearms fanatic" handcrafted bullets to be used for vintage guns like Smith & Wesson revolvers and antique, obsolete-calibre revolvers - including St Etienne.
He also smuggled a Colt pistol made for U.S. law enforcement agencies into the United Kingdom in November 2013 that was used the following month to shoot dead a man at a Christmas party in a London nightclub.
The genuine antique weapons imported by Edmunds were converted by him into killing machines because he was able to manufacture bullets.
Edmunds used a middle man, respected physiotherapist Mohinder Surdhar, 58, who he had met at a gun fair, to supply his weapons and ammunition to criminal gangs.
Edmunds was found guilty of transfer prohibited firearms and ammunition following a trail at Birmingham Crown Court.
Ammunition made by Paul Edmunds in the garage of his home
Edmunds was also found guilty on two counts of perverting the course of justice in relation to doctoring his firearms register in an attempt to cover his tracks.
Police have revealed the lethal legacy of an antique firearms dealer who supplied weapons used in gang crime, as they said more than 200 of his guns could still be on the streets.
"But this was no TV drama - these were real weapons; real bullets; real victims".
Both men are due to be sentenced in December.
The licensed gun dealer used his "encyclopaedic knowledge" of firearms legislation to exploit loopholes and smuggle hundreds of banned weapons from the US. Their actions have had a devastating impact on communities by fuelling violent crime, leading to fear and bloodshed. Surdar also had an armoury at his home and we believe Edmunds was teaching him the art of bullet making.
"Our investigation has undoubtedly prevented many more firearms and countless rounds of ammunition getting into criminal hands. and in all likelihood saved lives".
Rodgers, added: "Edmunds claimed he had no idea Surdar was passing the guns to criminals. It's hard to overstate the significance of these convictions: we have cut off a major firearms supply chain and one that's been used by unsafe men to commit serious offences".