Do you want to learn more about muzzle gas phenomena?
As it leaves the muzzle, the projectile is followed by what appears to be a violent eruption of propellant gasses. ‘This eruption is called muzzle blast. The blast is a gas activity that adheres to a specific sequence of events. It is a jet of short duration formed by hot, high-pressure gasses that follow a well-defined series of stages as it grows and decays.
Descriptively, muzzle blast is a system of normal and oblique shock waves that form the boundaries of the region in which the principal expanding and cooling of gasses occur. Surrounding the shock boundary is a hard shell and outside this shell is a turbulent “smoke ring” that moves radially and advances.
The main traveling shock is formed in the air by the released propellant, gasses when they flow past the projectile and induce a succession of weak shocks in the relatively still air just behind a much weaker projectile-induced shock. This sequence soon merges into a strong shock ahead of the projectile.
In the meantime, the projectile, by interfering with the direct gas flow, causes a strong shock to form behind it. This shock eventually becomes the quasi-stationary usual shock and with the oblique shock, forms the central supersonic region, dubbed shock bottle, of the jet. The flow that goes into the bottle begins at the muzzle where the gas is glowing.
This visible light, extending only a short distance, is called primary flash and may be white light, indicative of actual burning, or it may be the red glow of bright solids in the gas.
On the other hand, the gas moving ahead through the normal shock decelerates to subsonic velocity, flatten, and thus has its temperature elevated to approximate that at the muzzle. This temperature is high enough to cause intermediate flash, a red or reddish-orange cone of light.
Ignition may also be due to preflash
A phenomenon not usually associated with muzzle blast since it precedes the projectile from the barrel. It is the burning of low-pressure gas that has leaked ahead of the projectile while still in the bore. If the leakage is copious and the burning duration long, the air-gas mixture can overtake it and thus become ignited. Gas leakage of this nature usually happens only in used guns and is not considered a major problem.
Flash is a by-product of muzzle blast and, regardless of its appearance or intensity, does not significantly affect the development of the jet which is split into two periods — the growth and decay of the shock bottle. Although gas discharge from the gun decays steadily, the activity of the bottle offers a convenient vehicle for a qualitative analysis of the sequential events.
Raising of Dust Via Gun Blast
The raising of a dust cloud when a gun is fired too near to dry ground involves raising the dust off the ground and its ensuing scattering. Two forces are responsible, the pressure gradient surrounding the dust particles, and the drag of the gas as it moves past them.
A muzzle blast contains both. The shock that precedes the blast prepares the ground by loosening and raising it a short height. The high-speed central jet then scours the surface, picking up the increased dust but not diffusing it to any great extent. The upward drift of the blast’s dust-laden eddies is very slow. However, the highly explosive gas that surrounds the innermost jet, which is the “smoke ring,” speedily uplift the dust high above the ground. The rarefaction wave that follows also picks up and carries dust to considerable heights.
Gun Gas Deflection by Muzzle Brakes
The passages in a 308 muzzle brake are treated by the one-dimensional theory of nozzles, without allowance for friction at the walls. Furthermore, the gas is assumed to load the nozzle fully; true only if the nozzle is so devised that there is no interruption away from the barriers. To prevent this, the semi-angle of a conical nozzle should never exceed 30°, a rather large angle. Smaller angles result in larger nozzles, thereby increasing a 308 muzzle brake weight. If more weight can be tolerated, a smaller semi-angle of about 20° is preferred. Semi-angles below 15° offers no considerable advantage over their immediate larger counterparts. Check it out here: www.madhousedesign.com/product/308-muzzle-brake/
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