We use a long hammer drill bit that is the same size or a little smaller than the pilot bit on the core hole drill and drill it all the way through the wall before we use the core drill. If you take the time to set a torpedo level and a framing square (on the bit), the pilot hole will be level and square. Once the pilot hole is established, the core drill pilot bit just follows the pilot hole all the way through. When you get close to the other side of the wall stop and start drilling from the other side of the wall. This will will eliminate any blowout of the concrete or block.
Originally Posted by Speshulk
Core Bore makes a nice hand held unit, its wet drilling though. They are a much cleaner hole than the dry hammer bits