Yes Bruce, you can use a G27 barrel (.40 sub compact) in your G33. I have a storm lake. Mags are fine for .40 as the 357sig is just a necked down .40. I have recently had a change of heart about the 357sig, worried about over penatration. I will switch out these barrels as needed, probably using .40 for everyday use and throwin in the sig for outdoor excursions. I need to find a place where I can do more field testing on penatration of various materials. I will post as I learn more.