The short answer is that bump keys are common key
blanks that have been cut down to the lowest depth across the blade,
though the individual stations, or spaces, have been preserved by
leaving a separator between each station. This is simply
accomplished by cutting each station with a code cutter, moving to the
next, and then cutting the adjacent station in the same manner.
This leaves a 'hump' or 'point' between each successive
station. As the key is inserted, and also as it is withdrawn,
the bottom pins are automatically bounced upward as the blade, with all
these raised separators, travels beneath them.
With the added use of tapping (rapping) while the bump key is moved
back and forth, and with a slight degree of turning tension applied
simultaneously, it is possible to bounce the bottom pins enough that
the percussive method of lock picking is brought into play.
This is roughly the same action that takes place when a pick
gun is used, but it takes much more practice.
Bump keys, surprisingly, are so popular today that they are found on
web sites that have little or nothing to do with the Locksmith trade.
It is likely that those who purchase these keys on a lark,
with no real interest in learning how to pick locks as a viable part of
becoming a Locksmith, soon loose interest because acquiring skill with
them is no less difficult -- and perhaps more so -- than learning how
to use "legimitate" lock picking tools.
We offer them because there IS a place for them in a Locksmith's tool
kit, if only as a last resort.
