Muzzle Flash...

[ny32182]

I have a few questions about muzzle flash.

First, what exactly causes it? I know powder that doesn’t burn to completion is at least partially responsible, but I’ve also heard that the gases coming out of the barrel are so hot that they combust some of the oxygen in the surrounding atmosphere, thus contributing to muzzle flash. Is this true?

Second, how exactly does a flash suppressor work? The theory I heard one time was that the expanded chamber of the flash suppressor allowed the superheated gasses coming out of the barrel to expand slightly before being fully exposed to the atmosphere, thus cooling them to the point where they couldn’t ignite ambient oxygen. This makes sense I guess, but doesn’t take unburned powder into account. Any other explanations?

Third. It seems that different brands of ammo produce vastly different levels of flash. I’m talking specifically about AR’s now. I have never run Wolf .223 in my guns. Always Winchester white box, PMC, or now, GA Arms 55gr fmj. All three of these loads produce a large flash that is easily seen even in broad daylight, with bare postban muzzles on my 16 and 20†guns.

Last week at the range, I was shooting my superlight, and the guy at the other end was shooting a 20†HBAR. I noticed while it was still light out, that there was no visible flash whatsoever out of his gun. As it got dark, all I could see was maybe a dime size ball of very faint orange flash coming out of his barrel. This was a far cry from the basketball sized white fireballs that my guns launch with each shot in low light situations. I inquired as to his ammo, and it was Wolf. Any particular reason for this?

 

[Mike Irwin]

Muzzle flash, as you note, can be caused by burning powder being ejected.

It can also be caused by the powder gasses themselves becoming incandescent -- a plasma.

A flash suppressor I believe normally works best on the second kind of muzzle flash. It forces the powder gasses to mix with air and cool below the point of incandescence.

 

[benEzra]

Among the combustion products are carbon monoxide and possibly other combustible gases (hydrogen?) since the combustion is generally somewhat oxygen starved. So some secondary combustion occurs when the initial gases hit atmospheric oxygen, producing essentially a faint flame front.

(And no, you don't get carbon monoxide poisoning from shooting.)

 

[Sleuth]

Composition of the powder is a major factor. Much of the US GI ammo sold as 'surplus' failed the flash inhibitor tests. There is a chemical added to mil spec powders to reduce the flash. The generic ammo is cheaper because they don't add these to the mix.
A box of "white box" will usually have much more flash than a box of real USGI. The flash supressors I have seen work by breaking up the gases into smaller amounts (M1A, M16/AR15, M60, M240B&G), reducing the flash into smaller parts. They do not have expansion chambers.