Approximately 25% of the population is under 18 years old.
There are approximately 115 million households in the US.
Persons under 18 years, percent, 2011 23.7%
http://quickfacts.census.gov/qfd/states/00000.html
Subtracting from 100 yield a percentage of 76.3% over the age of 18
313,914,040 (76.3%) = 239,516,415
And 47% of that yields: 112,572,713
I would submit that the other various factors cancel each other out.
Example – two people in the same household with a gun could be considered to own said gun – co-owners if you will.
As to the type of gun – old, new whatever I would say that isn’t a factor knowing that the Statists won’t be happy until they’ve taken them all.
Then there is the underestimation of the survey data from over a year ago – given the facts of recent events and the tendency for a fair number to not self-report.
Given all those factors, I would say the figure should be around 114 Million gun owners back when the survey was taken, and around 120 Million now.
How does that sound to Y’all?