Is the P99 available in other calibers? Are any interchangeable?

Yes. In addition to 9mm (9mmx19) and .40 Auto, the P99 is also available in 9mmx21, but it is not currently being imported into the US by Walther America. Earl's Repair Service does offer this caliber at a considerable premium price.

Important Note: Changing calibers or otherwise using aftermarket barrels in your P99 (or P99 QA or P990) is not endorsed by Carl Walther (Germany) or Walther America (US), and will thus void your warranty.

Prototypes chambered in .357 Sig were made, but never went into standard production. Bar-Sto, however, is now manufacturing .357 Sig conversion barrels that will fit only the .40 Auto version. The barrel change is all that is necessary to shoot .357 Sig. The slide, frame, recoil assembly, and magazines stay the same. Bar-Sto may also begin to manufacture 9mm conversion barrels for .40 Auto P99s. The following are three photos of an actual Bar-Sto .357 Sig conversion barrel for the Walther P99, shown side-by-side with a factory Walther P99 .40 Auto barrel, along with two photos of one of these barrels installed into a Walther P99:

    

In addition, Bar-Sto is manufacturing 9mm conversion barrels for P99s chambered in .40 Auto.

Jarvis is currently manufacturing P99 barrels chambered in 9mm, .40 Auto, and .357 Sig. Their barrels are also available in threaded and ported configurations. Contact them for more details.

Rumor has it that there will be a .45 Auto version of the Walther P99 produced.

The 9mm and .40 Auto P99 barrels are not interchangeable due to different dimensions, as follows:

  • Barrel tube diameter: 0.5875 inches for .40 Auto versus 0.5475 inches for 9mm
  • Barrel hood width (extends to the breech face): 0.4235 inches for .40 Auto versus 0.3935 inches for 9mm

    This effectively means that a .40 Auto barrel is too large, diameter-wise, to fit in the hole at the end of the 9mm slide, and its barrel hood is too wide to fit in the breech face.

    The 9mm barrel is also too short to fit into the .40 Auto slide.

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