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Glock G20 .40 Conversions

The Glock model 20 is a full-sized pistol chambered for the powerful 10mm bullet. This model was a contender for widespread use among law enforcement until a model chamber for the slightly shorter .40 S&W caliber bullets gained popularity. The G20 cannot be converted. Conversion between calibers is possible between Glock pistols chambered for .40 caliber ammunition and those designed for the .357 SIG bullet. For example, the G22 is a full-sized pistol chambered to use .40 caliber ammunition and can be converted to fire .357 SIG bullets by simply switching the pistol's barrel with one from a G31 (the full-sized .357 SIG Glock pistol).

Convertible Calibers
- The 10mm bullet used by the G20 is similar to the .40 caliber bullet, but the length of the shell casing prevents conversion to any other caliber. Among Glock handguns, two calibers can be converted: the .40 S&W and the .357 SIG. The .40 S&W bullet was developed by Smith and Wesson in the late '80s as a hybrid between the powerful .45 ACP and the smaller 9mm. The .357 SIG was designed by SIG Sauer as a high velocity .357 bullet for semiautomatic pistols. While the projectiles vary slightly, the shell casings are exactly the same.
Convertible Models
- Only comparable Glock models in .40 and .357 calibers can be converted one to the other; do not attempt this procedure with any other calibers. The full-sized .40 pistol is the G22, which is compatible with the G31. The compact convertible models are the G23 in .40 caliber and the G32 in .357 SIG. The subcompact convertible pistols are the .40 caliber G27 and the .357 G33.
Necessary Parts
- To convert calibers, you will need a barrel. For example, a G22 needs a barrel from a G31. You must use barrels from comparably sized models; for instance, you cannot place a barrel from a full-sized model into a subcompact model. Since the shell casings are the same for both bullets, the magazines are compatible and do not need to be replaced.
Procedure
- Unload and field strip your pistol. Remove the original barrel, and replace it with the new barrel. Reassemble the weapon to successfully switch calibers. Remember only to shoot the ammunition for which the barrel is designated. Never shoot .357 SIG bullets through the .40 caliber barrel, since it can damage the weapon and possibly cause injury.

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