Essentially the forward edge of the chamber locks into the ejection port, thereby removing various complex machining operations from the production process. SIG simplified this, using a method that has become extremely popular in the years since, with manufacturers such as Glock adopting it. This locked the slide and barrel together, until a swinging link (on the Colt 1911) pivoted the barrel downward, thus providing the delayed blowback operation.

This method required cutouts in the hood of the slide, together with locking rings on top of the barrel that fit into the cutouts. For decades pistols had been designed using the method developed by John Browning for delayed blowback function (necessary with cartridges that produce a substantial degree of pressure upon firing). It contained many innovative features, the most innovative being the method of locking. The end result, adopted in 1975, was the 9mm SIG-Sauer P220, known in Swiss Army service as the A75. SIG entered into a collaboration with the German arms company Sauer to develop a new pistol.

So they turned to the local Swiss company SIG, previous maker of guns for the Swiss Army, for the answer. The problem was that the SIG P210 was simply too expensive to manufacture, and the Swiss Army wanted something cheaper, but still capable of providing excellent performance, as well as having a double-action trigger. The story of the P225 really began in the late sixties, when the first signs that the Swiss Army might want a new pistol began to emerge.

Sig p229 year of manufacture