Getting the longest life possible for your core bit is key if you want to run a productive and profitable drilling operation. Changing a drill bit takes time especially the farther down the hole it is, and the time spent replacing a bit is not useful.
Choose the right bit for the hardness of rock you will be drilling in. The hardness of the ground is measured according to Mohs Hardness scale, a chart of relative hardness of various minerals. The scale consists of numbers one through ten; 1 being the softest and 10 being the hardest. Drill matrices are developed to perform ideally within a certain range of the scale so you need to pick a bit suitable to the hardness of the ground to be drilled. There are tools that help you identify the hardness of the ground such as an Etcher kit or scratch test. See a video on how to determine rock hardness here.