A compact version of the P226, the P228, is in use with various law enforcement agencies and also with the US military, where it is designated as the M11. The P228 has a shorter slide and barrel than the P226. Unlike the P226, the P228 is available only in 9×19mm Parabellum with a 13 round magazine, but can also use P226 15 or 20 round magazines. Aftermarket magazines extend the capacity of the P228 to 15 rounds. From a distance, the P228 can be differentiated from the P226 by comparing the trigger guards (the P228's is curved, while the P226's is slightly hooked) and the barrel and slide lengths (the P228's barrel 99 mm (3.9 in), thus having a corresponding shorter slide). Also in a side by side comparison the P228 would appear slightly shorter (15 mm (0.59 in) shorter) than the P226. The larger capacity P226 magazine can also be employed in the P228 although it extends from the base of the grip. Civilian sales of the P228 were discontinued with the introduction of 9mm chambering in the P229 but was recently reintroduced in limited quantities to civilians with an accessory rail and designated P228R. The P229 is nearly identical to the P228, however its slide is made from milled stainless steel (vs. the P228's forged carbon steel slide) and is available in 9mm, .40 S&W, and .357 SIG. In the summer of 2012 Sig Sauer announced they were releasing the M11A1, which is essentially the P228 with a short reset trigger, Sig Lite tritium night sights, MecGar 15 round magazines, and a military style smart tag and serial number. Later in 2012, Air Force M11b versions of the P228 were released for civilian sales. It's rumored that 50 of these were released. The M11 is to be replaced in the Army and Air Force through the Modular Handgun System program.
The all-metal P228, like the other members of the SIG Classic family, operates by the locked breech short-recoil method pioneered by John Browning. On firing, the slide and barrel are locked together for a few millimeters of rearward movement, after which the barrel is cammed down at the rear. By this time the bullet has left the barrel and the pressure has dropped to safe levels, whereupon the slide completes the rearward stroke, ejecting the spent cartridge. The recoil spring then propels the slide forward, stripping a round from the magazine and in the last few millimeters of forward movement the barrel is cammed upwards, locking the slide and barrel together again. Instead of the locking lugs and recesses milled into the barrel and slide of other Browning-type weapons (such as the Colt M1911A1, Browning Hi-Power and CZ 75), the P228 locks the barrel and slide together using an enlarged breech section of the barrel locking into the ejection port. This modified system, which was devised by SIG based on Charles Petter's Modèle 1935A pistol and their own SIG P210, has no functional disadvantages compared to the original system, and has since been copied by numerous firearm manufacturers. The slide of the pre-1996 P228 was a heavy gauge, mill finished sheet metal stamping with a welded on nose section incorporating an internal barrel bushing. The breech block portion was a machined insert attached to the slide by means of brazing and a roll pin visible from either side. Since 1996, production has shifted to CNC machining and the slide is now milled from a single piece of stainless steel. Therefore the current standard P228 has a black anodized, stainless steel slide. This resulted in a stronger slide, which was necessary to chamber the more powerful .40 S&W and .357 SIG cartridges. The frame of most models is made from hard anodized aluminum alloy. The standard SIG P228 incorporates a decocking lever on the left side of the frame above the magazine release button, which first appeared on the Sauer 38H prior to World War II, which allows the hammer to be dropped safely. In chambering or firing a round, the actuation of the slide automatically cocks the hammer. By using the decocking lever, the hammer can be de-cocked without actuating the firing pin block, making it impossible to accidentally fire the weapon by using the decocking lever. Furthermore, using the decocking lever makes the weapon "drop safe", which means the firing pin will be blocked from striking a loaded round unless the trigger is pulled. Pulling the trigger and slowly lowering the hammer does not make the weapon "drop safe", and can result in an accidental discharge if sufficient force is applied to the hammer. Properly decocked, the pistol can be holstered safely and can be fired in double action mode by simply pulling the trigger. The SIG P228 has no manual safety. Double action trigger pressure is approximately 44 N (10 lbf). Subsequent shots are fired in single action mode with a lighter trigger pressure of approximately 20 N (4.5 lbf). As with other DA/SA pistols such as the USP and Beretta 92FS, some training is required to minimize the difference in point of aim caused by the different trigger pressure between a first double action shot and subsequent single action shots. The hammer may also be manually cocked at any time by the user to fire in single action mode.