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Old February 23, 2012, 06:51 PM   #23
Slamfire
Senior Member
 
Join Date: May 27, 2007
Posts: 4,070
Surplus powders are a risk. A risk that the stuff will go bad in the can before you know it.

Gunpowder has a shelf life. A rule of thumb is 20 years for double based, 45 years for single based. Thee are a number of accounts of 1980's vintage single based factory IMR powders going bad.

Half of all the surplus IMR 4895 I bought went bad. I had to toss about 700 LC Match 308 cases because the nitric acid gas released by the powder cracked the case necks.

Considering the powder was about 80% the cost of new and all the components that got scrapped, I lost money.

Look guys, the primary reason these surplus powders are on the market is because the "master" test sample went bad, or the cartridges in storage were tested, and the powder was shown to be at the end of its shelf life. The reject is 20% of stabilizer left in the powder.

Section from the Propellant Management Guide:

Stabilizers are chemical ingredients added to propellant at time of manufacture to
decrease the rate of propellant degradation and reduce the probability of auto ignition during its expected useful life.

As nitrocellulose-based propellants decompose, they release nitrogen oxides. If the nitrogen oxides are left free to react in the propellant, they can react with the nitrate ester, causing further decomposition and additional release of nitrogen oxides. The reaction between the nitrate ester and the nitrogen oxides is exothermic (i.e., the reaction produces heat). Heat increases the rate of propellant decomposition. More importantly, the exothermic nature of the reaction creates a problem if sufficient heat is generated to initiate combustion. Chemical additives, referred to as stabilizers, are added to propellant formulations to react with free nitrogen oxides to prevent their attack on the nitrate esters in the propellant. The stabilizers are scavengers that act rather like sponges, and once they become “saturated” they are no longer able to remove nitrogen oxides from the propellant. Self-heating of the propellant can occur unabated at the “saturation” point without the ameliorating effect of the stabilizer. Once begun, the self-heating may become sufficient to cause auto ignition.



I only learned this a couple of years ago, I am shooting up the surplus IMR 4895's that I have as fast as I can. I will admit what I have that is good, it shoots exceptionally well, but I am not sitting on it as I don't want to pour it out on the lawn after it turns red.
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