I had a machine shop center up and weld a normal bit onto a piece of straight 48" drill rod. I have them in 5/16, 3/8, and 7/16. They were dirt cheap and work perfectly. Any straight bit will put a 9" deep hole right where you want it so long as it is aimed correctly...if your ramrod groove is pointing the bit up into the barrel or out the lock mortise, don't be surprised when that's where you wind up.