Brass round head screw from the hardware store, coat the head with non-embedding grinding compound and while spinning on the crown make a figure 8 with the drill, next figure 8 is 45 degrees to the first, and so on. The key is keep the drill motor moving and do not spin in place. It will make a good crown. I've 'fixed' bad crowns on high power bolt action unmentionables with this method and they stack bullets. Is it as good as an indicated and lathe cut crown? 99-1 no, but likely will shoot as good as whatever gun you do it to was going to anyway.