I have a Glock 20 and a KKM .40 S&W conversion barrel for it. KKM also makes a .357 Sig conversion barrel for the G20. They also make 6" barrels for the G20 in 10mm, .40 and .357 all for about $165 each. The G20 with the .40 KKM is extremely accurate and works all the time. I am very happy with my KKM. I have put about 2000 rounds of .40 through it since once fired brass for it is easy to come by (I reload). The 10mm magazines work fine for .40 and I am told they also work for .357. I have made loads from 230 ft-lb to 700 ft-lb and they have all worked fine in the G20 with the factory 17 lb recoil spring. It takes almost 15 seconds to change barrels on the G20. Just be sure you have the right cartridges in the mag.