I was watching a show about repo men on the Discovery Channel, and saw one of the guys using a Curtis key cutter (“key gun”) to clip a blank and make a key for a GM ignition lock cylinder. The use of the cutter itself isn’t my concern, as it seems pretty straightforward. But in order to know how to clip the key, he did something that looked like jiggling the key in the lock. That is what my question is about.
He would insert the key in the lock, pump it in and out rapidly a few times, look at it and start cutting. He repeated a couple of times, and ended up with a working key. He said something about tumbler length, and appeared to be looking for markings to tell him about the pins, but what exactly was he doing? I’m familiar with the mechanics of locks and the basic principles of conventional lock picking (i.e. with torque wrench and picks), although I couldn’t do it to save my life. But I can’t figure out what useful information the guy was getting by pumping the key.
Of course, I only ask out of intellectual curiosity. There are much better ways of bypassing a lock, should I want to. Personally I’d be better off with a brick and some good old-fashioned hot-wiring.