Powder Burning - the long and short of it

[PaulS]

I have seen more posts that claim you need a long barrel "to burn all that powder" in such and such cartridge than I can stand.

I guess I just want to see how many people actually know that the powder is all burned in the first few inches of barrel length and the pressure remains high (as does the heat) that continues to accelerate the bullet down the long barrel.

PaulS

I hope this doesn't start one of those forever debates.

[KN]

Then explain the fire ball coming from the end of the barrel after dark.  KN

[Zachary]

This could get very interesting...both of you have made good points.  I just don't know the answer. :?  

I don't think, however, that this would be one of those heated debates because, unlike true heated debates like "what is the minimum caliber for elk" (which there is no scientific answer), there MUST be some scientific - hard-and-fast answer to the question of powder burning.  Again, I'm no scientist, or even close to it, so I don't know.

I wonder - if a barrel was 100 inches long, would there still be a fire blast at the end of the barrel?

Zachary

[tominboise]

John Barsness in Rifle magazine had an article in a issue about this very subject.  It's called something like "Barrel Myths".  He debunked the slower powder requiring a longer barrel etc.  All the powder is consumed in the first few inches of barrel, and if slow powders outperform faster powders in a particular cartridge, they will continue to do so even in shorter barrels.  I don't remember the particulars about the muzzle flash, but it had something to do with chemicals in the gas oxidizing when exposed to the atomspheric pressure.  I can't look it up until this weekend cause I'm on the road in Florida, but will post when I get back home.

Should make for an interesting thread.

[Zachary]

Tom,

I live in Coral Gables (Miami area).  

I heard about all of the cold and snow in the north.  I bet your glad to be down here in sunny (and WARM) Florida.  :-D

Zachary

[SeanD]

I greatly respect John Barness, and im sure hes right, but when shooting slower powders out of my 19.5 inch barrel 30.06 i was shooting a flame out the end of the barrel at dusk, when i switched to a faster powder the flash went away.  Anyone have an idea why?

[PaulS]

When the powder burns it produces ash and high pressure gasses that are heated to about 3000 degrees F. Slower powders hold the pressure longer than faster powders. When the pressure goes away so does the heat. When the heat goes away so does the glowing ash and gasses. The fireball of muzzle flash is the glowing gasses left over from combustion and not powder still burning. The easiest way to demonstrate the difference is to fire a cartridge without a bullet after firing one with a bullet. (be sure to clean all that powder residue out after the no bullet round is fired) Unburned powder has more mass than the gasses do and will travel in a ballistic path (like streamers coming out of your barrel) but the gasses build a nice ring or ball that seems to just dissipate in a short distance.

PaulS

[Paul H]

The more accurate statement would be that the new "super mags" require a longer barrel to take advantage of the extra powder capacity, or std mags not offering any performance advantage in short barrels.  If you're buring an extra 20% powder and gain all of an extra 100 fps for a ~3% gain in velocity, then it seems like a poor tradeoff.  If you use a 28-30" barrel, and gain an extra 300 fps over the std mags, then you've actually made a gain.

It isn't an accurate statement to say all powder is burned in the first couple inches of barrel travel, as some loads can leave unburned powder in the barrel and/or be ejected with the bullet.