Exploding bullets

To return to the subject of explosions, and in particular the issue of "Detonating Gunpowder", I have just come across a set of books by Marshall on Explosives written both during and immediately after WW1, when huge quantities of black powder were still in use.

He comments of a series of studies on the role of sulphur in the combustion process, and points out that it's function is far from clear. The most obvious function of sulphur is to lower the ignition point. How it does this is not that clear, as the ignition point of a mix of sulphur and saltpeter is 470F, charcoal and saltpeter is 320F whereas all three as black powder ignites at 290F! He considers sulphur to act as a form of catalyst, with nitric oxide and hydrogen sulphide being formed as intermediate products.

Much of how gunpowder performs is down to it's physical structure. A typical "corn" of gunpowder is made from a compressed mass of finely ground ingredients, mainly influenced by the charcoal content. Charcoal is an extremely porous substance with an enormous potential surface area. It is highly adsorbant (hence its use in respirator filters) and even when ground acts as a substrate for the potassium nitrate and sulphur crystals.

It would appear that a gunpowder explosion is, at least initially, dust based, with a flame front expanding through the gaps between the corns, breaking them up and causing further release of dust. Only when the dust ignites does the process move to the gas phase. Marshall observes that gunpowder does not ignite in a vacuum, (which I was not aware of!). and which goes to support the "dust phase" argument.

This is not the same process as a typical high explosive. Here the fuel and oxidiser elements are not physically discrete, but bound together in an unstable molecule. The detonation process is tied up with the breaking up the molecular structure by the shock wave, which in turn is sustained by the chemical reaction that ensues between the molecular elements... This is an intrinsically chain like runaway reaction and has the temperature and pressure dependent attributes of a classic detonation..

Gunpowder appears to have a fundamentally different reaction whereby an essentially air supported dust based reaction initiates the process, which then runs to a gas based reaction after the initial breakup of the corned structure. This would tend to explain the rapid, but essentially limited gunpowder deflagration process, and the fact that corned powder burns faster than fine meal powder!

...every day a school day!
 
Very interesting, does he explain the differences between the various natures of charcoal when used in corned powder? BP appears much faster and consistent when pressed in a "barely damp" condition prior to corning. This is in marked contrast to pressing "wet" or for that matter dry, however different wood or rye charcoals make a difference to the burn speeds prior to pressing and corning.
 
Very interesting, does he explain the differences between the various natures of charcoal when used in corned powder? BP appears much faster and consistent when pressed in a "barely damp" condition prior to corning. This is in marked contrast to pressing "wet" or for that matter dry, however different wood or rye charcoals make a difference to the burn speeds prior to pressing and corning.
He notes that the best charcoal used in India at Kirkee and Ishapore was made from dal stems (cajanus indicus - The Pigeon Pea), and that a lot of the cheap powder used for mining and quarrying was made by itinerant workers from Bukus (adhatoda vasica). At Madras the wood of the milk hedge (Euphorbia tirucalli) was used. The Afghans apparently used vine cuttings! - who knew they grew vines!

I know in the UK, Waltham Abbey used williow (Salix Alba),Alder Buckthorn (frangula alnus) and alder (alder glutinosa) for making charcoal. The best was considered Alder Buckthorn which was used for small arms gunpowder.

The need to maintain a certain level of moisture in the incorporating mill was well understood. The water formed an emulsion with the tarry elements in the charcoal and held the saltpeter in a supersaturated state. The amount of water seems to have been left to the skill and judgment of the mill man. From looking at film of incorporating, it seemed only enough to keep the green charge damp. I seem to recall the test was to squeeze a handfull of powder and see if it clumped..

Powder making in India and China works on a different principle. Here the powder is incorporated in large bowls and kept very wet while it is worked by hand. In China, they even heat the pans to dry out the charge. The final drying is done in the sun.. this is mostly for firework powder and produced something much weaker than western corned powder...

Charcoal made from straw and lignite was used to make "brown powder" which has a (slightly) lower burn rate than black, and was used for the very heavy guns of the 1890s to try and keep the breech pressures under control. Gunpowder was also pressed into large "Prism" pellets to slow down the burn rate, but both these processes were only partially successful. It was not until colloidal nitro propellents such as cordite and ballistite cam along that proper control was gained over burning rates.
 
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MoleBath

LE
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Really? Wouldn't that be a waste of scarce ammo?
It was a standard German tactic to have 1 or at most 2 SF guns firing tracer high and other MG34/42 SF guns firing non trace at a lower level. Takes a bit of fiddly work at last light in a defensive position but effective. Reported by a number of historians
 

Cutaway

LE
Kit Reviewer
It was a standard German tactic to have 1 or at most 2 SF guns firing tracer high and other MG34/42 SF guns firing non trace at a lower level. Takes a bit of fiddly work at last light in a defensive position but effective. Reported by a number of historians
Links ?
 
Another question if I may HE, does he comment anywhere on any calculations used in loading boreholes with BP for quarry work? I was looking into this some time ago but found nothing written. It would be interesting if Marshall had collated any thoughts on the issue.
 
As this is the most current weapons thread I would like to ask a question of the illustrious arrserati.

I live near Longmoor Ranges and am quite used to the sound of rifles (and the bleedin Chinook that likes to hover over my place).

The rifles just tend to go “bang” but yesterday morning someone was firing single shots of something that went “thwock” (a bit like the noise a tennis racket makes when it hits a ball). It was distinctly different to a rifle shot.

Any clues on what it might have been?
Bullets make a thwock sound when hitting flesh, or more of a thunk. Maybe ... Errr... some 'live' targets were being employed? :-D:jocolor: (the above question should be considered a 'joke' by the way!)
 
Sounds like a 40mm grenade launcher.. firing prac rather than HE as it would sound Thwock.... Bang!
 

Cutaway

LE
Kit Reviewer
Bullets make a thwock sound when hitting flesh, or more of a thunk. Maybe ... Errr... some 'live' targets were being employed? :-D:jocolor: (the above question should be considered a 'joke' by the way!)
On reception by live end users I've found that rds often elicit a shrieking sound or choice swearing.

Not yet sure if it's tgt or slipstream dependent.
 

Cutaway

LE
Kit Reviewer
Sounds like a 40mm grenade launcher.. firing prac rather than HE as it would sound Thwock.... Bang!
Oddly enough I've never come across a 40mm HE blind, your experience may differ and new gen would be appreciated.
 
Oddly enough I've never come across a 40mm HE blind, your experience may differ and new gen would be appreciated.
No.. provided you are aiming at a hardish target, they are pretty reliable.. there are several 40mm grenades in service and the latest versions are a vast improvement on the original 60s types..

Most modern 40mm fuzes have a self destruct funtion which initiates the main charge if nothing has happened after (say) 10 seconds. This reduces the number of blinds drastically, which is good as they are bloody hard to find...
 
I know in the UK, Waltham Abbey used williow (Salix Alba),Alder Buckthorn (frangula alnus) and alder (alder glutinosa) for making charcoal. The best was considered Alder Buckthorn which was used for small arms gunpowder.
Buckthorn Alder is what the Swiss use and their powder is widely considered to be the best. It's cleaner burning (still leaves loads of crud!) and around 10% more energy by weight. It also costs an arm and a leg. Having used el cheapo powder I can confirm the cleaner burning.
 
Heh. That's nothing. Remember the old demonstration of how flashbangs were not to be fucked with, by the expedient of sticking a lit one under the old tin helmet and near sending it into orbit? Or was it that the mad as hell mental Scottish branch of the Army Cadet Force were the only ones that did that one?
Saw it done with an old-fashioned galvanized steel dustbin lid on the cadet leadership course at Thetford. Maybe the TA (the peak of my illustrious military career) was a touch less mental than the cadets?
 

Cutaway

LE
Kit Reviewer
No.. provided you are aiming at a hardish target, they are pretty reliable.. there are several 40mm grenades in service and the latest versions are a vast improvement on the original 60s types..

Most modern 40mm fuzes have a self destruct funtion which initiates the main charge if nothing has happened after (say) 10 seconds. This reduces the number of blinds drastically, which is good as they are bloody hard to find...
Cheers.

But hard to find ?
What have you got against kicking all sorts through the bush ?
 

Cutaway

LE
Kit Reviewer
My old Regiment would have probably rammed a MOULD kit into the bin, stuck it on top of a hill, hooked up a generator to it, got comms working from it.

And then put a thunderflash into it and blew it up.

...

Wait, I should have said my old Troop would have done that.

After stealing, err, I mean borrowing it and painting it blue.
 
To return to the subject of explosions, and in particular the issue of "Detonating Gunpowder", I have just come across a set of books by Marshall on Explosives written both during and immediately after WW1, when huge quantities of black powder were still in use.

He comments of a series of studies on the role of sulphur in the combustion process, and points out that it's function is far from clear. The most obvious function of sulphur is to lower the ignition point. How it does this is not that clear, as the ignition point of a mix of sulphur and saltpeter is 470F, charcoal and saltpeter is 320F whereas all three as black powder ignites at 290F! He considers sulphur to act as a form of catalyst, with nitric oxide and hydrogen sulphide being formed as intermediate products.

Much of how gunpowder performs is down to it's physical structure. A typical "corn" of gunpowder is made from a compressed mass of finely ground ingredients, mainly influenced by the charcoal content. Charcoal is an extremely porous substance with an enormous potential surface area. It is highly adsorbant (hence its use in respirator filters) and even when ground acts as a substrate for the potassium nitrate and sulphur crystals.

It would appear that a gunpowder explosion is, at least initially, dust based, with a flame front expanding through the gaps between the corns, breaking them up and causing further release of dust. Only when the dust ignites does the process move to the gas phase. Marshall observes that gunpowder does not ignite in a vacuum, (which I was not aware of!). and which goes to support the "dust phase" argument.

This is not the same process as a typical high explosive. Here the fuel and oxidiser elements are not physically discrete, but bound together in an unstable molecule. The detonation process is tied up with the breaking up the molecular structure by the shock wave, which in turn is sustained by the chemical reaction that ensues between the molecular elements... This is an intrinsically chain like runaway reaction and has the temperature and pressure dependent attributes of a classic detonation..

Gunpowder appears to have a fundamentally different reaction whereby an essentially air supported dust based reaction initiates the process, which then runs to a gas based reaction after the initial breakup of the corned structure. This would tend to explain the rapid, but essentially limited gunpowder deflagration process, and the fact that corned powder burns faster than fine meal powder!

...every day a school day!
L believe that most German WW2 stick grenades used black poweder as the charge.
 

Cutaway

LE
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