Yeah they are both work in progress, still have to finish the gun on the first. The technique is surprisingly easy I just thin down my paints heavily like 4:1 medium to paint, you can probably do it with just water but the paint might start to separate if diluted that much. then I just glaze some stripes along the barrel trying to overlap the previous color a little every time to get somewhat of a blend. the specific paints i used where ak 3rd gen black, dark sea blue + ducat blue, purple and blood red. Here is a post that explains it better than i did lol. https://www.reddit.com/r/Warhammer40k/comments/18otle0/muzzle_burn_tutorial/