A while back, I got a 9mm barrel for my G32 to permit cheaper practice. It runs like am absolute top, even with the cheap 115gr WWB loads. I have encountered one issue, however - the slide almost never locks open on an empty magazine. I have had this problem with both 115gr WWB and Winchester NATO ball ammo. The NATO spec stuff will lock open SOMETIMES, but not very often. Is there a difference in recoil spring weight between the .357SIG and 9mm? If so, is it enough of a difference to cause the failure to lock open. The 9mm G19 mags I am using are brand new, so I doubt it is an issue with the magazines, and (as far as I know, as I got the gun used) it still has the factory recoil spring installed.