Some say 9mm will function in a .40 mag I say BS.
That's why I said "may" above. I've seen someone load a 40 mag with 9mm and shoot it. I was surprised that the rounds stayed in the mag so I tried it (loading, not shooting). It stayed in one mag but not in my others
Can't tell you why but the mag in question functions fine in my 40 caliber Glocks. But, I did mark it just in case