Best data I have seen has about 9/10 of NICs checks are new guns in circulation.

EXAMPLE:

My CHL permit requires a check, but I have bought 2 stripped lowers on another.

But some are for interstate sales of used guns (I bought a Savage 99 that way).

Then I renewed the CHL and that was another Check.

So I have about 20 NICS check for 18 new guns.

"The Church can and should help modern society by tirelessly insisting that the work of women in the home be recognized and respected by all in its irreplaceable value." Apostolic Exhortation On The Family, Pope John Paul II