First, except for a few guns stolen from package services and dealers that were never sold, legally or otherwise, virtually every gun sold in the United States was legally purchased – by a law abiding citizen. Second, criminals are businessmen of sorts. They operate under the same constraints any other business is run – but the business is illegal. Every business must keep costs down. Guns are like any other tool to a criminal. They are disposable. As prison surveys have invariably found; the object is to be as well armed as possible for as little money as possible. Third, if we can find either the percentage of legally or illegally purchased guns used in crime we can subtract that from 100 and obtain the other percentage. And fourth, most of the guns that were legally purchased and that were then used to commit a crime are “one crime and out” deals. Most of the stolen guns that are used in crimes are used in a great many crimes. So we have several ways to take the question implied in the search.
I haven't seen any statistics but ill guess 99%of the firearms used in crimes are legal weapons. I will guess 50% of those weapons were purchased illegally. The rest were either stolen or legally purchased.
Are you asking what percentage of crimes are committed with a legal gun or what percentage of legal guns are used in crimes? Most crimes are committed with legal guns, and very few legal guns are used in crimes.
13 percent of all arrestees say they had stolen their gun. The most common method is straw purchases, where another person makes the purchase and then transfers it to the felon, and the second is illegal activity by people with Federal Firearms Licenses (FFL). The rough numbers based on various areas is 40 percent are straw purchases and 30 percent are illegal sales by FFLs. see: http://www.pbs.org/wgbh/pages/frontline/shows/guns/procon/guns.html