I've long-suspected that the ~300 million number was too low. Just estimating off of casual firearm owners I know in the USA, they tend towards 2 firearms per person. Assuming I only know people from the non commie-cuck half, that's ~300 million guns right there. Once you account for collectors and regular shooters instead of just a couple guns in the closet, you end up with a massive number of additional guns. 600 million sounds far more plausible even at a gut-check level.