Pure honesty, 9mm in a .40

[Proud Southern Son]

It’s a P229. You can shoot 7.62 in it and it’ll be fine.

 

[WestKentucky]

That is part of why I use visibly different bullets in similar but different calibers when I’m loading visibly similar rounds. 9 in a 40 is a wake up call, just be careful not to let it happen again with rifle rounds. AR mags are easy to slap into a gun with the wrong ammo present, and can jam a gun up quickly, or worse let you touch off a short fat round in a bottleneck chamber.