What do you think? The fact that the .357sig worked perfectly in the 9mm mags. I'd venture to bet that if you do this extensively, you may end up wearing your followers where they may not feed the .357 100%. Now---that's just a wild guess on my part, and I don't mean to elicit any feelings of paranoia here as to what or about what I'm talking about.
What is interesting? The fact that the .357sig worked perfectly in the 9mm mags, or the fact that I would have to ask such a question after owning a Glock for 4 years?