The surveys are mostly borked as far as gun ownership.
For example, if I ask "Do you have a gun in your home?" the answer is quite different from "Do you own a gun?" which is in turn different from "Is there a firearm on your property?".
Another interesting trend - during a Democratic presidency the number of people who refuse to provide an answer aka "No Opinion" to a question of ownership increases significantly. I think it would be safe to assume that the majority of those who refuse to answer the question do in fact have a gun at least on their property.
This poll breaks it down and no, it hasn't changed much in the past 25 years.