I bought 1000 rounds of Winchester M22 the day after the Sandy Hook shooting, at the time, they had another 12000 rounds I could have bought, but didn't. Those other rounds were gone the next day.
Once I found out that there was a run on ammo, I immediately starting buying reloading components. If I couldn't buy 22LR, at least I could make my own centerfire stuff. I managed to get a pretty good stash of powder, primers and bullets before they started drying up, especially small rifle primers and .223 bullets. It was almost two years before the components starting becoming more available, but at greatly inflated costs. Because I had no immediate need, I was able to hold on long enough for prices and availability to be more reasonable and I bumped up my stash quite a bit more.
The day after the Orlando shooting, I went into high gear stocking up on components and also managed to snag some pretty good deals on 22LR while I was at it.
I'm not stocking up for an EOTWAWKI, I just want to have enough ammo to shoot when I want to shoot. As it stands right now, I've got enough ammo and/or components to probably carry me through the next several years and if push comes to shove, at least I've got quite a bit of trading material, if it ever comes to that