FAQ from Sig Sauer..Can I convert my 9mm SiG to .357 SiG or .40SW. Unfortunately our pistols (with the exception of the P250 and the .22LR Classic Series) cannot be converted to or from 9mm. Changing between .357SiG and .40SW is easily completed in most cases with just a barrel change(239-357/40 also requires a magazine change). [/color]