McCoy Chuck was a really genius design. The jaws ride in machined grooves. This ensures that they are always in alignment and grip the shaft of the drill bit evenly and tightly. Since there are no springs, when you loosen the chuck, jaws don’t come apart automatically. They use gravity to slide down the grooves. This means that you may need to give the drill bit a little twist so that the jaws loosen and slide back. The chuck should always be clean and well lubricated. This is the key to it working well. As long as you do that, this chuck will last for a very, very long time. I believe it will outlast any other design especially one with springs.
Note that the drill shaft for the chuck on a lot of Millers Falls drills Including models 2, 5, 980, 1980, and many others have 22tpi and are 7/16 in diameter. An unusual size indeed. 
