Carbide tip 10" drag bit with 3 1/2" pin. These bits cut fast and aggressive.The drag bits take more torque to turn than roller cone style bit.
Down the whole hammers are absolutely the world's fastest way to drill rock. If you have a lot of drilling jobs and you're making plenty of money this is a way to go. But It is much more expensive to use. A rotary mud rock bit depending on the size are 200 to 700 dollars. Down hole hammers prices are from 2500 four A four inch hammer, to 6500.00 for a 8 inch hammer. Also there's not just the down hole hammer to consider. To run the hammer you must have a large air compressor as large sea CFM output. The deeper you drill with the down hole hammer and the larger the borehole you drill with the down hole hammer the more air cfm it takes. So if you already have a drilling rig that is rated for air, the larger the compressor the better. To drill rock fast, you will need a down hole hammer, and a large enough air compressor to run the hammer and keep the whole clean. Drilling hard rock with the down hole hammer does make things much faster though. I've seen people with portable drilling rigs that they couldn't get through the rock where they were, and only getting 6 inches to 2 foot per day, with standard rotary bits. But the same setup with the 4 inch down the whole hammer gets 75 ft in 4 hours without power down. With power down its even faster.