Something is going on. After 9/11, Americans started buying non-hunting type guns in unprecedented quantities (and that got really wild after Obama's election, with an ammunition shortage that's not ended (confounding factor for the latter, it's after the time the Cold War stocks of surplus military ammo got exhausted)).

There are confounding factors, e.g. America is aging as the huge demographic bulge of the Baby Boomers age, and that especially combined with a nationwide sweep of shall issue concealed carry regimes has resulted in a lot of these older folk, perhaps realizing they're less able to physically protect themselves, buying guns and getting concealed carry permits (my class for that in SW Missouri was overwhelmingly middle aged or older). (If Puerta v. County of San Diego is upheld, which is the way to bet, 90% of the nation's population will be covered, already it's much easier to list the few states that don't do shall issue.)

ADDED: but that doesn't explain the run on rifles of military utility....

I think a factor was the government's response which essentially told us we were on our own (more details if desired).

But this is fine grained hard data, due to the taxation regime for guns and ammo (used to fund hunting favorable conservation stuff, ranges to a certain extent and perhaps more of than going forward, etc.), here we don't have to depend on anecdotes, surveys, etc.