Recently got a battery powered rock drill for TAPCONS. Tested it on pure limestone yesterday as an acid test for use in concrete. Drilling was fine with 5/32" rock bit. But near the end of screwing in the 3/16" x 1 3/4" anchor, the head torqued off. Tried it again slowly and got in about 1" before chickening out. Does anybody know of a "screwable" anchor that would work better?