A friend has bought a 5D tactical jig to mill ar15 and AR10 lower receivers. Has made ENOUGH AR15s and AR10s, he says he doesn't need any more. And after a little counting i agree with him. I intend to build some that is not a 223, like a 6.5 Grendel or 7.62-39. I am trying to think of a way for him to continue to use his jig. I know that there are some 50 BMG rifles that use an AR15 lower. Are there any others? He is a self taught machinist and is pretty good at it so some thing that we/he can build might get him to going on a new project.