I've started making my own gun effects with a little advice from @songrobin LED Flame Accessory DIY Tutorial although I'm not using LEDs. I'm using spherical acrylic beads and perspex rods. To attach them to the gun I either drilled a hole in the barrel or enlarged the existing one. The mottled effect was done by adding a very watery coat of a different colour over the previous colour. The water's surface tension causes it to clump up. Here I've put the last coat on not thick enough to cover what's underneath and done it in a helical pattern. Making this one was way more trouble than it was worth and I almost gave up. I don't think I'll be making one for this right arm. I'm not happy with these ones, I think they look too much like flowers.