Pyroxylin and semi smokeless

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Ah yes, where things get obscure. After smokeless powder was invented, it was quick to perfect. But in between the last serving days of Joe Black (a name I definitely did not just decide to give to BP at this instant for creating this excessively lengthy and sarcastic joke) and nitrocellulose, people were caught up in other inventions that bridged the two worlds.

Semi smokeless powder is rarely discussed, mainly because it saw little if any military service, and its formulation is seldom explained. Who knows if they were even referred to as semi smokeless. Today, mixing BP and SL is considered highly hazardous. Well, one confirmed use of semi smokeless was in the Austro Hungarian straight pulls, for an early version of the 8x50mmR Mannlicher. Designated 8mm M.1890 scharfe-patrone. It fires a 244 grain bullet at 1950 fps. What it used for propellant is something I have yet to figure out. Whether it was a mix of smokeless and black powder, or something entirely.

Another form of supposed semi smokeless might be the obscure Schultze powder. Pellets of wood pulp nitrated and impregnated with Barium nitrate. It was famous for its time, but clearly it went into obscurity. Generally, this reveals something interesting, why did it need the extra nitrate. Well, I soon learned that nitrocellulose can be nitrated to a varying degree, and generally speaking the less nitrogen, the less potent, but the more safer. I then tried to find a term for lightly nitrated cellulose, which turns out to be used in later grades of film stock and modern day nitro cellulose products like ping pong balls, plastics and lacquers. Which is why they probably don't explode. The lightly nitrated cellulose is known as pyroxylin. It doesn't inspire confidence considering it has pyro in the name.

I wondered if manufactures of smokeless powders vary the degree of nitration in their propellants. It was inconclusive, but what I did figure out is that pyroxylin was intended as a safer alternative to fully nitrated cellulose. Another thing that I could only say was that when searching up Khyber Pass weaponry, I heard nitrate film stock was chopped up and used as smokeless powder.

Other than that. The only article I could find on lightly nitrated cellulose being used as a propellant is this:

https://www.scientificamerican.com/article/pyroxylin-or-gun-cotton/

It doesn't say very much, but it gets me thinking- would this make a form of smokeless propellant with operating pressures within the realms of early compressed black powder military loads?
 
Semi-smokeless is not a mix of BP and smokeless. It's just really poor smokeless. Very early smokeless power was exactly smokeless and some powders today aren't either. Bullseye, for example.
Gun Cotton is the common name for nitrocellulose. Schönbein, fiddling around in 1846, discovered, by accident, that cotton soaked in nitric and sulfuric acids then dissolved in ether and ethyl alcohol burns really fast. That became the basis of smokeless powders.
A Yahoo net search for 'Gun Cotton', turns up 7,590,000 results.
 
To address the OP, all nitrocellulose used in gunpowder is a mix of cellulose hexanitrate, tetranitrate, and mononitrate, but the majority is hexanitrate. The manufacturing process aims to make it all hexanitrate, but is never 100% successful at achieving that objective. You can, however decide which nitration level will dominate the resulting nitrocellulose by adjusting the ratio of nitric to sulfuric acid used in the process and probably by playing with temperature and other factors.

The reason hexanitrate is most desirable for powder is that its oxygen balance is best among the different nitrations. That is, all high explosives (and guncotton is one) have molecules which provide both fuel and oxygen for combustion when their atoms are knocked apart. The recombination during combustion makes gas, and whether the burn rate is controlled (deflagration) or violently rapid (detonation) depends on everything from grain geometry to deterrent coatings.

But here's the thing: all the nitrated cellulose forms have too little oxygen for complete combustion of the fuel molecules they have available. This is why unburned carbon is left behind in your bore. For hexanitrate the oxygen shortage is -24.23%, so it is said to have an oxygen balance of -24.23%. For tetranitrate it -44.42%. For mononitrate it is -76.38%. So using the lesser nitriations in powder intentionally means you need a heavier charge weight to get enough oxygen to burn enough fuel to make enough gas to get the bullet performance you want. That means larger capacity cases, more ignition difficulty, and a lot more powder fouling after each shot, none of which are desirable qualities for a gunpowder. This will apply to all the lesser alternatives.

Incidentially, nitroglycerin has an oxygen balance of +3.52%. This is why adding to smokeless powder to make a double-base powder results in higher energy content in the same volume. The nitroglycerin not only burns completely, it has a little extra oxygen left over to help burn a little more of the nitrocellulose fuel molecules.

Single-base smokeless rifle powders have energy content on the order of 4000 J/g. Black powder is at around 3,000 J/g. Tetranitrate, handled the same way as hexinitrate is, would produce a powder with just a bit over 2,000 J/g of potential energy content. So using pure tetranitrate would result in a powder weaker than black powder and you would have to blend it with hexanitrate just to match BP performance.

Cellulose hexanitrate by itself burns too rapidly to be safe in guns. It wasn't until deterrents and other controls like adding petroleum jelly (cordite) came along that it could be made safe and useful. Before that was fully achieved, partially nitrated propellants were tried, but for the reasons I mentioned for lesser nitration levels, this results in a dirty, low energy powder that black powder could often outperform. So they were intermediate technologies that fell by the wayside. There were some odd interim combinations, like black powder grains covered with guncotton fibers (Les-Smok) used in .22 rimfire.

As to why the other powders are not much discussed, that's not lack of military origin so much as the fact none is available from reloading supply vendors. This is, after all, the handloading forum section of the board, and people reading in this area don't generally spend a lot of time pondering components they can't use.
 
Well I do spend a lot of time pondering things of no use, but then of course as stated, at least hopefully, not here and bore people to tears.

On the other hand, that's a great write-up that I will soon forget the details but remember that there is a definite oxygen deprivation in most of it except nitro which is the give that keeps on giving (lots of movies based on it and good stuff for powder) .
 
Based on various other sources, and some speculation. I finally read up on the properties of nitrocellulose and various propellants. I read that a form of cordite, cordite sc has a reduced nitrate content in order to make it soluble without the assistance of acetone, which is used to dissolve high energy nitrocellulose. It was used in naval guns and artillery. I suppose this is an example of a low migration propellant. An even lower energy example is booster charge rings that are placed around the thin tail of mortar shellac meant to extend their range. But here is what confuses me, why do they use percentages to represent the degree of nitration?
 
"Semi-smokeless is not a mix of BP and smokeless. It's just really poor smokeless."

Incorrect.

Semi-smokeless powder, made by varying manufacturers, was a combination of gun cotton/nitrocellulose and modified black powder.

The most popular and widely used semi-smokeless powder in the United States, Du Pont's Lesmoke, was a hybrid combination of gun cotton and black powder.

Lesmoke was primarily used for .22 rimfire ammunition, but was available in other cartridges.

https://books.google.com/books?id=Q...Q6AEIMTAC#v=onepage&q=du Pont Lesmoke&f=false




I know King's Semi-Smokeless powder was available to handloaders, but I've never found any indication that Lesmoke was available commercially other than in loaded cartridges.
 
The percentages I cited are only for oxygen based on how much oxygen you would need to get all the hydrogen, nitrogen, and carbon in the finished molecule oxidized to the usual gas species, with 0% oxygen balance meaning 100% oxidation with no left over oxygen (+ balance) and no shortage (-balance).

For the nitration itself, you could come up with percent nitrate (NO₃ˉ) radicals bonded to the final molecule as a percent of the total molecular weight. You could also declare that hexanitrate, having six of them, was 100% nitration and tetranitrate was 66.7% and and mononitrate was 16.7%, then work out the average for the species mix your process produces. I don't know which convention you saw. If you have a link, I can take a look.
 
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