Drop in bolt and 10 round magazine. Made by Ciener for Atchisson. Out of production. I don't use mine enough, so out it goes. Ran fine last I used it. $100.
I also have seven Black Dog 25 round .22 magazines that work with this kit. $10 apiece.
All for $150, which ends up being a free magazine to you. Photos emailed on request. Thanks for looking.