Twenty page report just released dealing with a large survey of state and federal prisoners and their usage of firearms during crimes (over 200,000 sampled). As suspected, a small percentage of state and federal criminals acquire their firearms from legitimate sources. Most common source is the underground market at about 40+% and then via theft/victim. About ten percent were acquired through licensed dealers. See Table 5 and 6. As suspected, longarms are not the weapon of choice for criminals and are employed about one percent of the time during actual crimes (folding state and federal offenses together). Not surprisingly, those committing violent crimes and public order offenses are more likely to report using firearms.
https://www.bjs.gov/content/pub/pdf/suficspi16.pdf
https://www.bjs.gov/content/pub/pdf/suficspi16.pdf