I remember after the Sandy Hook shooting, when everyone went nuts. .40 S&W was the last caliber they ran out of. And the first caliber they got back in stock. In that regard it might not be a bad idea to have at least one .40 laying around. I just have never been attracted to the caliber enough to buy one.... Even heavily discounted. It's easier to keep plenty of ammo in stock, and buy it when it's plentiful and cheap.
I never thought I would see the day when you had to buy ammunition the same way you buy stocks.... When no one wants either. It's like the whole toilet paper deal. Back when all the Corona crap started last March, they were stripping the shelves of it. Now it's stacked high, deep, and cheap. People are still wiping their asses with 6 month old stuff, they've got piled up in their closets.