I have a couple friends who bought those when they came out. Lots of issues, and returns for work. Only one kept his, as a safe oddity. I almost bit, till they started with issues.
OK, I remember that they changed the design of the bolt carrier tail, where the firing pin was located in, from a round style to a slant style........I also remember that if you had the old style bolt to send it to them and they would change it to the new style.If I recall, it was something to do with the bolt and or firing pin on both of them. It was a long time ago. I'll ask my FFL tomorrow. He sold and sent them back. I'll bet he remembers.