I have access to a gentleman who is an energetics expert. I asked him about smokeless powder lifetime. The whole topic is a subset of “Insensitive Munitions”. A term you can Google and find bits and pieces in the public domain.
Smokeless propellants are used in more applications that just cartridges. Rocket motors, explosive warheads, these all use smokeless propellants.
He told me that powder starts deteriorating the day it leaves the powder mill. The rate of deterioration of double based powders is governed by the Arrhenius equation.
http://en.wikipedia.org/wiki/Arrhenius_equation. The hotter it is, the faster it goes. Single based powders apparently deteriorate in a linear fashion.
What the expert told me was that double base powders are made of nitroglycerine (NG) and nitrocellulose (NC). The NG wants to wick its way, through capillary action, into the NC. Forming a lower energy state compound. In the process of combination nitric acid gas is released. As nature wants to go to a lower energy state, this reaction is inevitable. There are preventive stabilizers in the powder which eat up the nitric acid. The stabilizers get consumed over time.
Exposing powder to high temperatures for extended periods of time is bad. Heat accelerates the reduction-oxidation process.
Cool dry storage conditions, he actually said “artic”, are about the best for long term storage of powder.
The expert said that Navy powders are initially tested at 10 years. They put a litmus paper in contact with the powder. If the paper changes color, nitric gas is present.
If the paper shows a problem, they then chemically test the powder for the amount of stabilizer in the powder. If that drops below 20% original, than the powder is scrapped. You have to have the original powder records to know how much stabilizer was in the powder when it was made.
The Army scraps by clock time. Double based powders are scrapped at 20 years, single based 45 years.
A few years ago TALON released tons of demilled military powders. That stuff was at the end of its service life. Half of my surplus 4895 powders went bad. One keg turned red and was outgassing and it was poured out on the lawn. About 8 pounds did not turn red, but went bad in the case.
First indications that I had a problem were that I had a lot of split case necks on fired cartridges. Then case necks started to crack on unfired ammunition. When I pulled bullets, I smelt nothing, in the case or in the bottle, but I found green corrosion on the bottom of bullets. I believe that nitric acid was weakening the work hardened areas of the case, and causing corrosion on the bottom of the bullets.
Incidentally, the powder shot exceptionally well in cases that did not have case neck cracks. I shot some exceptional scores with the stuff at 600 yards with 168 Match bullets. I had "funny" retorts on some rounds. The expert said as the surface of gun powder changes, burn rates are affected.
If the powder changes color, it is bad. It is grossly bad. It was bad a long time before the color changed. And it is time to pour it out. That is when you typically see red rust in a metal powder can (acid gas eating the can up) and red powder.
I was told that when enough nitric acid is released, the powder will spontaneously combust. The expert diagramed the chemical reaction and hot spots can develop as energy is released. As the Military is extremely scandal sensitive, they won’t tell anyone that big bunkers have blown up, but they have. Ammunition depots go Kaboom all the time due to old ammunition spontaneously combusting. You can Google this and find incident reports in the literature. But you won’t find mention of some of the American ammunition incidents that this expert investigated. We Googled one incident he wrote a report on and found nothing in the public domain.
Government Rule #2: Minimize Scandal.
Water is bad for smokeless gun powders as it damages the powder surface and wicks NG to the surface. Even through age is reducing the total energy content of the powder , wicking NG to the surface will increase the initial burn rate of the propellant, which has lead to pressure spikes.
Contact with rust is bad for powders. As I understand contact with iron oxide increases the rate of the reduction-oxidation reaction.
The Navy used to store cannon powder in pools but the powder was to be recycled. I guess the water absorbed the nitric acid and kept everything cool, preventing heat build up. But the expert told me that the dry lifetime of powder is rapidly reduced after exposure to water.
