In a life time of pro-gun advocacy and activism, I have found two things that really turn around people on guns:
1. Take them shooting and show them how much fun shooting is and how nice shooters are, and,
2. People are confronted with a life threatening situation such as a riot, looting, or a personal attack on them. When they feel the heat, they see the light...so to speak.
I think this most recent spike in gun sales is an example of No. 2 above: People feel a sense of foreboding and feel threatened.