That is NOT what causes muzzle flash.
And, that is NOT how a flash suppressor works.
There are three types of muzzle flash: muzzle glow, primary, and secondary. Muzzle glow and primary flash are just the incandescence of the hot waste gas and are actually rather dim in comparison to the secondary flash. Unless the barrel is extremely short, less than 7 to 8 inches for a rifle like a .308 Winchester, all the propellant is burnt long before the bullet exists the muzzle.
The primary flash is just the glow of the super heated gas as it exits the muzzle
For secondary flash:
The combustion products of burning propellant are inflammable, they just need oxygen and an ignition source. When these gases leave the muzzle at high pressure, 4,000 to 12,000 psi and high temperature, 1300 to 2000 R, they expand adiabatically down to low pressure and temperature, actually over expanding far below atmospheric conditions until a normal shock wave sets in. Across the shock wave the pressures and temperatures rise again to the muzzle exit conditions. Within this region of the shock wave there is a large amount of turbulence which mixes ambient air with the propellant waste gas. Now in the area of the shock wave we have the three things needed for combustion, fuel, air and a heat source, so you get a nice ball of flame. If you look closely at a muzzle flash, you will note that it is always separated from the muzzle by some distance.
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The way a flash hider/flash suppressor works is to prevent the shock wave from forming, or reduce the intensity of the shock wave to minimize the temperature rise. The best way to do that is to absorb energy from the muzzle gas through making it move the tines of a prong, duck-bill, or cage type flash hider. The other type is the cone type flash hinder which works by controlling the expansion of the gas, the can (WW2 BAR) type is a less effective version of the cone. The M16 cage-type flash hider is actually a combination of both the cone and tine types and very effective.
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