Buy copper plated .22 rounds, almost as cheap as the lead ones, but they dont leave lead in your gas tube. Firing the .223 rounds blows any residual lead out of the gase tube, and right into your bolt carrier. Used kits go for approximately $100 with a Slick Willy mag, new can be had for about $150 with a Slick Willy, $180 for new kit with a standard magazine.
Kharn