I will say this too, it does not seem to be just restricted to guns and gun websites. There are a few Jeep forums I frequent and they too have been dwindling in traffic and posting. I have dropped down to visiting them once a week, as there might be 1-2 new posts a day, and not worth visiting every day. These same sites just a few years ago were booming, and you had a full page or more of new posts every day.
AR15.com forums seems to be slowing down some too, with the exception of the general discussion section where there are endless threads every day about doom and gloom, they are coming tomorrow to take them all from you, they are taking over, blah blah, blah. The actual technical forums seem slow.