https://www.cnn.com/2018/02/15/politics/guns-dont-know-how-many-america/index.html
1. We don't know how many people own guns
There is no countrywide database where people register whether they own guns (the law doesn't allow it). We have to rely on surveys instead. High quality telephone polls from Gallup and the Pew Research Center in 2017 found that 42% of people in the US live in households with guns. According to the General Social Survey, which has a much higher response rate than telephone polls and interviews people in person, a relatively lower 32% of Americans said in 2016 that they lived in household with guns. The gap between telephone and GSS surveys has existed in some form for 20 years, so it isn't just a one-off difference.
It's not clear which datasets are more correct. The GSS, with its high response rate, is generally thought of as the gold standard survey in understanding social trends in America. It is conceivable, though, that people may not want to admit to owning guns to people who are standing in front of them."