I thought it was something new in semi-automatic handgun technology, but Queen Tam has pointed out that other people have used this same technique in other designs. So it's just business as usual, because most everything that people have been doing with guns for the last umpteen years are just refinements or variations of already well-understood techniques. Still, the technique is new to me, and I've already posted this, so we'll just go on.
When a gun is fired, the explosion of force pushes the bullet down the barrel, but it also produces an equal pressure rewards on the shell. In order to get most of the force to work on pushing the bullet, you need to keep the shell in the chamber at least until the bullet has left the barrel. This isn't very long, you might be able to measure this time in microseconds, but it's kind of important.
In automatics there have been two main mechanisms for keeping the shell in the chamber after it has been fired. One is by making the breech block (the chunk of metal that holds the shell in the chamber) big and heavy and putting a hefty spring behind it. This is only practical for smaller, less powerful rounds. 22's and I think most 380 caliber automatics, use this principle.
The other is to make a complicated latching mechanism the keeps the block locked to the barrel until some very tiny time consuming action has taken place. The German Luger, the American 45 and the Browning Hi-Power all use their own particular way of doing this. It makes the guns complicated and expensive.
Walther CCP Mechanism
Walther's method uses the high pressure gas produced by the explosion to push against a piston that retards the motion of the breech block. In effect, the gas is pushing on two things in one direction: the bullet and the piston, and only one thing in the rearward direction: the breech. It's also pushing on the frame in the rearward direction, but you are holding onto that piece with your iron grip so it's not going anywhere. It's also the piece in which all other action is compared.
Inspired by View From The Porch.