On skeeter size bugs maybe 5 feet. The sea salt is coarser and will kill bigger flys out farther. If you are going for big bugs then use a bigger grain salt and get as close as you can without scaring them off. Salt looses its velocity rapidly and that is the idea behind this gun, It makes it safe to shoot in the house and does not hurt walls, woodwork, pictures, windows, screens, or grandson tushies. 
To test your aim and the pattern of your gun at various ranges sight it in on aluminum foil. Foil dents easily and will show you where you are shootin' and when your shooting to far away to expect proper pattern density and penatration. IT"S FUN!! I did test it out on slugs like Anika wanted me to. You know what happens to slugs when you put salt ON them. Try seeing what happens when you put salt IN them. 
MMMMMM, foamy.
Go git 'um. DC
To test your aim and the pattern of your gun at various ranges sight it in on aluminum foil. Foil dents easily and will show you where you are shootin' and when your shooting to far away to expect proper pattern density and penatration. IT"S FUN!! I did test it out on slugs like Anika wanted me to. You know what happens to slugs when you put salt ON them. Try seeing what happens when you put salt IN them. MMMMMM, foamy. Go git 'um. DC