Flame from a gun muzzle is generally depicted as a teardrop shape with the fat end at the muzzle getting thinner as it travels away.
In reality it\'s mostly closer to that shape, but thinner. (it also depends on the length of barrel, calibre of weapon etc...)Also the rifling of the barrel, which imparts the spin giving ballistic accuracy to the projectile, causes the gases to form a very tiny twist to the muzzle flash. Also the expulsion gases are White Hot not red.
Flame throwers/Flamers project the fluid under pressure before ignition, so you get large ragged teardrop shape narrow end at the muzzle. One thing to remember is that the fluid has weight and will drop with gravity, while the flames will still go upwards.
If I remember what I was told correctly Flamthrowers crews were always taught to arc the flame, for maximum effect.
Most Importantly Never point them into the wind! (need I say more!).
Take a look a Victoria\'s Eldar Fire Dragon for one of the best flame effects.