Questions about the ignition/deflagration/detonation of black powder?

R

Robert Nicholson

CGN Ultra frequent flyer
Rating - 100%
9   0   0
Location
Okanagan
My recent interest in forts with cannon has made me think about how cannon or any old black powder gun achieved explosive force.
My research (wikipedia) tells me that oxidizers in the powder provides that neccessary component to achieve the fast burn needed.
But I have trouble visualizing how old touch hole/flash hole ignition systems could generate the needed compression to detonate the load.
My imagination prefers to see a fast burn coming out of the flash hole rather than detonating the powder charge.

Anyone have a short, easy to understand description of the physics behind how flash hole ignition works?
 
Robert Nicholson said:
My recent interest in forts with cannon has made me think about how cannon or any old black powder gun achieved explosive force.
My research (wikipedia) tells me that oxidizers in the powder provides that neccessary component to achieve the fast burn needed.
But I have trouble visualizing how old touch hole/flash hole ignition systems could generate the needed compression to detonate the load.
My imagination prefers to see a fast burn coming out of the flash hole rather than detonating the powder charge.

Anyone have a short, easy to understand description of the physics behind how flash hole ignition works?
Click to expand...

Black powder is an explosive. It will explode, if you pile enough of it out in the open and provide ignition. It does not deflagrate like the powder used in reloading, which is technically, a propellant, and needs to be contained to provide the needed speed of burning to propel the bullet down the barrel.
That it is actually an explosive, is one of the reasons that a lot of gun stores do not handle it, even if they stock reloading stuff. Different regs apply.

It does not need 'compression' to ignite, it needs enough heat, either from a fuse, an igniter using something along the lines of a percussion cap, which is a fast moving flame, or by dint of sticking a red hot piece of wire down the touch hole, igniting the powder charge.
After which, it all happens very quickly.

Inside the chamber of a cannon, the flame front that begins, expands and ignites the powder that is around it, and so on.

Once the charge is ignited, the pressure builds faster than the gasses can bleed out the touch hole (which they do) causing the pressure to build (which also causes the ignition front to move even faster through the remainder of the charge) until the projectile or whatever other material which has been resisting the expansion, gives way, usually in a very loud fashion. Time frame measured in milliseconds. Boom.

Methinks you are misunderstanding the very basic principles behind the introduction of fire to gun powder.
 
Very good! Thanks to Trevj for the written explanation of the more explosive nature of black powder.
And thanks to Wendell for the informative and entertaining video, especially the part pointing out the ejecta from the touch hole.

Also formed an appreciation for the robotic and stylized movements of the loading crew in order to be safe and load correctly.
 
Google Black Powder Factory Explosions. Entire towns have been wiped off the map.

Also, consider that the big guns on WWI and WWII battle ships used BP charges. Been more than a few ship born magazine explosions catastrophes.

Pretty potent stuff.

M
 
Last edited:
gnmontey said:
Google Black Powder Factory Explosions. Entire towns have been wiped off the map.

Also, consider that the big guns on WWI and WWII battle ships used BP charges. Been more than a few ship born magazine explosions catastrophes.

The stuff is pretty potent.

M
Click to expand...

And fireworks, probably the single largest users of black powder on the planet these days! They tend to use a lot more of the very fine powder grades of BP. Which ignite easier. Cannon powder is extremely coarse by comparison. Which slows the rate of burn, else the cannon could easily get....unwell! Which they did often enough anyways.

I will point out that they were not firing with any wadding over the charge, to get it to make the amount of a bang that it did. Figure out what kind of a blast the vent would be putting out if it had a cannon ball to move, rather than just the column of air it was in that video. Erosion of the vent hole was a very real problem over the expected life of a cannon, much as it is in BP rifles. Liners were often installed, sometimes of non-corroding materials like platinum.

If you did that with, say, pistol powder, you would see a fizzling flame out the barrel, and naught-all else. Same if you poured the same size piles on the ground and lit each. The BP would flash up with a whump (think old fashioned Western Movie Photographers, with their flash powder) of varying intensity depending on the coarseness of the BP grains, while pretty much any reloading powder that is not sealed inside some form of containment, will simply flare up and burn rapidly. Explosion, in the case of BP, a deflagration, in the case of what we normally use to reload with.
 
Its a complicated subject. Detonations are very extreme and violent events where a shock wave propagates through an exothermic reaction, generating and picking up energy. This reaction is too violent to be harnessed in a gun or cannon - think of modern bombs. Accordingly, the process used by black and smokeless powder is a hi-speed deflagration, giving them the classification of a low-explosive. The possible exception is the very rare circumstance of SEE with smokeless powder. The tremendous black powder explosions stated above are often dust explosions, which can happen in sugar refineries, coal mines etc. These are caused by the rapid deflagration of a large volume of very fine particles. (Black powder can be very reactive due to its fine granules, moreso than smokeless powder which is engineered to a controlled reactivity...)
The building of pressure with a flash hole is explained above. If you want to learn more google the various subjects.
 
Last edited:
You must log in or register to reply here.
Back
Top Bottom