Likely it's just people that already have a gun, buying up more of them.
I'm certain that's some of it, it's certainly true for ME.
![grin =D](http://www.armedpolitesociety.com/Smileys/default/grin.gif)
And the anti's are definitely working hard to sell the narrative of the "nuts" hoarding and doubling-down with ever more guns, while the number of individual owners is forever shrinking as a proportion of the population.
However, it's lunacy to try and explain away the massive deluge of NICS checks as being all existing gun owners. At a minimum, being conservative, I'd think it's reasonable to guess the swelling numbers of NICS transactions indicates the percentage of gun owners, or gun-owning households is remaining steady, if not slowly growing.
And taking into account secondary transactions, such as gifts, private sales, inheritance etc. there's going to be a non-trivial rate of redistributing firearms to new owners even if the initial NICS transaction was an "existing owner".