I found this chart of more recent information I found this chart of more recent informationDidn’t scroll down far enough to see that.
It looks like at most 11% of prisoners could have bought it through a straw purchase. That would assume all guns bought through gun stores, pawn shops, and gun shows were straw man purchases. It’s certain prior to their crime at least some of the felons were still able to purchase a legal gun. So saying straw man purchases are a common source of illegal guns seems a stretch.