So... it looks like this Harvard study directly contradicts the other Harvard study.
What the survey does not do, and cannot do, is measure the number of gun owners who will not tell other people, that they own guns.
Surveys that ask if people would tell survey takers if they have guns shows the number to be about one third of gun owners.
That puts the gun owner number at about 30% instead of 22 percent. It is in line with the under reporting of total gun numbers that the survey found; they say 265 million.
Manufacturing and imports put the number closer to 400 million.