The Bill Drill is supposedly named after the inventor, some guy named Bill, although which Bill is not clear. Most say it's either Bill Jordan, Bill Rogers or Bill Wilson. Since it is a six-shot drill and Jordan was a wheelgun man, I think the evidence might suggest he started it, but who really knows? Truthfully, it was probably some guy named Pete who realized the "Pete Drill" didn't have the same ring.
Using a standard IPSC target at 7 yards, the starting position is either surrender—hands above your head—or hands at your side. At the buzzer, draw and fire six shots as fast as possible, but make them accurate. Only "A" zone hits count. You must have all six in the "A" zone for it to be a clean drill.
The Bill Drill trains for several things. First is a fast draw. It also trains for a fast trigger finger for rapid follow-up shots. It teaches recoil control and—most importantly—the kind of sight-picture discipline that allows you to put rounds on the target.
Most shooters have a tendency to go for speed when they first start this drill, which often results in poor sight alignment and misses. The key is to focus on your front sight and to work on developing a cadence where the trigger breaks at the exact moment the sights are aligned. By firing six shots, the difficulty of maintaining concentration and sight control increases exponentially. While it's tough to maintain a correct sight picture for each shot in a double tap, it becomes even more difficult as you transition through four more shots. There is a strong tendency for the shooter's concentration to decay with each successive shot. This drill works on fixing that problem. The idea is to learn to move away from spray and pray to delivering a focused, disciplined six shots on target.
Once this is mastered—if it ever is—you can increase the difficulty of this drill. One way is to move the target farther away, or use a smaller target like the target's head box. Another variation is to fire six, reload, fire six more, reload, ad infinitum. You can choose to shoot 12, 18, 24 or however many shots in multiples of six your heart desires and budget can withstand.
For the basic Bill Drill the most commonly stated goal is to run it in 2 seconds. Bear in mind, accomplishing that would make you a master-class shooter, so don't be disappointed if your time is somewhat slower. Most good shooters can do it in 4 seconds, and a reasonable goal for mere mortals is 3. I did find one video on the Internet where a guy did it in a scorching 1.11 seconds. I don't recommend you look up the video—it'll only get you depressed. But, we need to check this guy's DNA, because I doubt he is human.