Glock 23 magazine.. will 9mm ammo fit?

Hi Everyone;

Unclefo1123 here....

i am a 1st time owner of a Glock (or any handgun for that matter)...

My son bought the same exact model etc as mine about a year ago. He also purchased a 9mm Lone Wolf for it so he can afford $$ to shoot it when he wanted to (so did i just very recenty), the .40 ammo we bought is for home defense mainly.

Anyhoo... he told me i needed to buy a 9mm magazine for it, but when i went to the gun store where i bought the gun, the salesman seemed a little confused about that idea. he said he was pretty sure the original .40 magazine would work with the 9mm ammo... so he took some 9mm ammo and put it in the .40 mag, and it appeared to fit... but my son seems to think that i still need to buy a separate magazine.

i went online and one guy said it would fit, but that the 9mm ejects differently and will hit me in the head / face.

if anyone can help me, i'd really appreciate it. i don't want to spend more money on a magazine if i don't have to.

thank you