To begin with, nitrocellulose powders require a solvent to gelatinize them so that they can be formed into balls, flakes, cylinders, or strips. Single base powders are typically an ether-alcohol colloid of nitrocellulose. Double base powders are made from nitrocellulose and nitroglycerine and use ether, ethyl acetate, or isooctanol, as processing solvents. Much of this solvent is lost in processing. The solvent must remain at the minimum level to keep the propellant from becoming brittle and losing plasticization causing the powder grains to turn to dust which will raise pressure dangerously as the smaller the fuel the faster it burns. Just look at how much faster a pile of wood shavings burns than a big log does. Without a certain amount of solvent, you cannot keep the dimensional stability of the powder grains.

This solvent will also act on primer compounds, rendering them incapable of detonation. Because of this, the mil-spec limit for residual solvent in the dried powder is 0.25 weight-% (0.25% of the powder weight). If this limit is exceeded, the life of the primer will be shortened accordingly. These solvents off-gas from the powder and are what you smell when you open a powder can. Back in the days of the Army Coast Artillery, the powder magazines contained so much ether that many thought it was put there deliberately to somehow preserve the powder when, in reality, it was just massive amounts of off-gassing in a confined area.

For handloaders, use powder that does not exceed the mil-spec limit for solvent in dried propellant. Then, when making your cartridges, shield the primer from the solvents and acids. This was done in the past by the military as shown in the Army’s production drawings of the .45 ACP and 30-06 ammo. Note the part labeled “Seal, case vent” between the primer and the powder charge. That seal is a ten thousandth of an inch thick celluloid plug. It was installed by inserting a strip of ten thousandth of an inch thick celluloid over the primer pocket before seating the primer. The primer punches out the celluloid plug when it is installed, and it stays in place. Ammo thus sealed does not go bad. This is a very cheap and simple solution that anyone loading ammunition can employ regardless of whether you have a big factory with giant plate loaders turning out millions of rounds or a simple Lyman tong tool for reloading.

Handloaders can source these celluloid strips from Flannigan at Sabot Designs LLC, who I previously mentioned above. Flannigan has agreed to sell these strips to any individual handloader or ammunition manufacturer that wants them. Once in place, the primer is protected from the solvents and acids from the propellant powder, so things always go bang when they are supposed to.