rickomatic is spot on. There are a LOT of people who are scared of what the future may bring. In addition to those of us who are already gun owners, the number of folks buying their first gun is significant, and those folks are buying ammunition to feed the new guns. The customer base that we are all used to has expanded hugely, and it appears the manufacturers underestimated the post-election "surge".
As the economy slid into the tank, and as ammunition prices ramped up, a lot of gun owners who had been toying with the idea of reloading suddenly got serious about it. Moreover, those who already reload suspected the component prices would follow the finished ammunition prices and started buying powder and primers ahead of the price increases. In November I paid $120 for the 8-pound container of Varget that MinnMooney recently saw at $150.