This is a genuine surplus German HK G3 .22 caliber conversion kit. These kits fit and converts all HK91 and G3 rifles to shoot the more affordable .22 LR ammunition. The kit comes in the original green wooden case and includes bolt group, barrel tube, magazines, and cleaning kit.
We took this kit in on trade for one of our rifle packages and have no use for it here. They typically sell for $600 so we thought we would offer it at a discount here at $500. We have never used this kit and do not have any experience with them, but will attempt to answer any questions you might have.