M9 to P229P226"The P226 was designed for entry into the XM9 [JSSAP] Service Pistol Trials, which were held by the US Army in 1984 on behalf of the US armed forces to find a replacement for the M1911A1. Only the Beretta 92F and the SIG P226 satisfactorily completed the trials. According to a GAO report, Beretta was awarded the M9 contract for the 92F due to better durability during endurance testing and a lower total package price. The P226 cost less per pistol than the 92F, but SIG's package price with magazines and spare parts was higher than Beretta's. The Navy SEALs, however, chose to adopt the P226 later after a repetition of failures with some issued Beretta M9s."
Beretta won because they had a plant in Maryland able to immediately tool up and make the pistols (important because the plant was on US home soil). Also, the Beretta was the better choice because it had been in production since 1975 and was a more fully developed design at the time than the P226.
The first prototypes of the P226 were made in 1980, and the initial guns were little more than the earlier P220 pistol adapted to use a double-column magazine [one of the prototypes actually used the Beretta 92 magazine].
Back then, Browning Arms imported P220s and sold them as Browning BDAs.
Because SIG-Sauer did not have a US importer, they entered into a deal with Saco Defense, Inc. of Maine to supply the pistols used in the US military testing.
They were substantially different in design from later guns. The frame for example had completely straight rails - guns after that had frame rails that were bulked up with scallop cuts in the rails to relieve stress. This was done because it was found during testing that the frame rails on the XM9 test guns cracked, and even after the redesigns they continued cracking until the metallurgy was improved.
Later, the military came up with another pistol requirement [mil spec] for General Officers, pilots, females with small hands, etc., etc.
P228 (M11)A compact version of the P226, the P228, in use with the US military, 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 9x19mm Parabellum issued with a 13 round magazine, but can also use P226 15 or 20 round magazines.
P229The P229 differs from the P226 in several respects, and was originally introduced to supplement and then replace the P228 by adding the .357 SIG and .40 S&W as available chamberings.
The P226 and P228 were originally manufactured using a stamped-steel slide on an aluminum alloy frame.
The P229's new CNC-milled stainless steel slide, typically colored black with a Nitron finish [from the new milling and stainless production capabilities found in the new U.S. SIG factory] was introduced to handle the higher slide velocities created by the .357 SIG and .40 S&W loads
The slide on the P226 was later redesigned in a similar fashion, and civilian sales of the P228 were discontinued in early 2005 because the P229 can be chambered in 9mm, .40 S&W or .357 SIG.
Changing between .40 S&W and .357 SIG is as simple as switching out the barrel.
Magazines shipped with .357 SIG models have a "necked" throat that will accept only that caliber.
Magazines shipped with .40 S&W models will accept either caliber.
The 9mm model cannot be converted to another caliber.
Seems to me that the P229 may have originally been developed in response to a federal solicitation for pistols for "Sky Marshals".
