Here's some videos of a gentleman that invented a piston type punching machine.
The first video is of the inventor going over some of the details of the machine.

http://www.youtube.com/watch?v=oNkao...eature=channel

Second video is of an experienced boxer giving a demonstration.

http://www.youtube.com/watch?v=RKgV2...eature=channel

Third video, is of the same boxer blocking body punches.

http://www.youtube.com/watch?v=MYKTU...eature=channel

There are more videos, but thought I would just post these few.