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Old 02-02-2015, 03:23 PM
edwardm edwardm is offline
Join Date: Jun 2010
Location: WA
Posts: 87

I have no idea what BL-32's composition is/was. I didn't find an MSDS for it in a brief search. So I went with something I am familiar with - IMR-4895.

'4895 is a single base powder, composed mostly of nitrocellulose (NC), with some diphenylamine (DPA), dinitrotoluene (DNT), and potassium sulfate.

DNT is your burn-rate modifier. It's something that varies greatly in at least the IMR stick powders (from 4-15% or so total weight). Potassium sulfate is a salt - it inhibits muzzle flash. Too much, if memory serves, though, will cause a burn-rate modifier effect. Memory is fuzzy on that one these days, but the sulfate is stable and the DNT is relatively stable as well. "Relatively."

DPA and NC are what we care about. NC is made by adding nitro (-NO2) groups (ester bonds) to cellulose. To do this, the cellulose is mixed and cooked in a bath of water, sufuric acid and nitric acid, creating the ester bonds, then neutralized, and sent on for further use. Despite neutralization, very miniscule amounts of oxides of nitrogen (nitrates) can still remain in the NC, and in the final powder product. When the nitrates mix with air or water, nitric acid can form. In addition, heat (energy input) causes the ester bonds of NC to break down, releasing more nitrates into the mix.

DPA is our hero here. DPA scavenges free nitrates in the closed world of our cartridge or powder container. With no free nitrates to roam about and mix with water vapor, nitric acid formation is prevented - but not forever. Eventually all the DPA is used up, forming other nitrogen compounds. The NC continues to break down over time, forming more and more unbound nitrates in a world full of oxygen and water!

The common nitrogen compounds at this point become nitrogen dioxide (stinky brown gas) and nitric acid (nitrates and water vapor). Nitric acid in a world of zinc and copper (brass) is bad. The acid reacts with the brass alloy, forming copper nitrate and zinc nitrate. Copper nitrate is the pretty blue stuff you found in and on the brass and copper jackets. Zinc nitrate is a whitish crystaline 'fuzz', which is why you often see both the blue color and the whitish fluff in cases like this. The extent and appearance of both will depend on the alloy itself, and the surrounding time and conditions for the ongoing reaction.

Made short and sweet, your primary propellant constituent (NC) is breaking down naturally, faster when there is heat energy involved. The components mix with air and water to form gas and acid. The acid in turn attacks the copper and zinc in the brass, and everything goes to pot.
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