First of all, they should have called them Gun Nuts because of the double entendre. They goofed on that one unless somebody else is already making Gun Nuts so the name was taken. *Googles* Well it look like Gun-Nutz used to exist, but the company went under. I'm as shocked as you are. Tac-Sacs do exist, although the entire sack and mount is molded plastic so they don't swing. These are Gunsticles, dangling plastic testicles that you can mount to any Picatinny or Weaver railed rifle. They make the perfect gift for the gun owner in your life who's struggling to imagine their rifle is a Transformer's penis. They come in black and dark earth (brown) and cost $20 a pair. For clarification, that's $20 for one unit: a pair of testicles, not a pair of a pair of testicles -- that's too many nuts, like a PayDay bar.
Keep going for a couple more shots while I cruise the web for battle axe nuts.
Thanks to Closet Nerd, who wants to know how many Gunsticles owners fondle their gun nuts when they think nobody is looking. My guess is 200%.