The Ignition Chain, Part 4: Does Light Degrade Black Powder?
We have established that our goal as competitive shooters is to eliminate variables. The greatest variable is moisture. The second is a poorly tuned lock. The third is a dull flint.
This raises another question: Is light an enemy of black powder?
Does a charge exposed to sunlight while loading, or a flask left on the bench, suffer degradation?
The direct answer is no, light itself does not "spoil" black powder. But the indirect effect of light is a critical, and often misunderstood, variable.
1. The "Photodegradation" Myth
Black powder is not a complex, light-sensitive polymer. It is a physical mixture of three chemically stable components: potassium nitrate (a salt), charcoal (carbon), and sulfur.
Unlike some modern plastics or smokeless powders that can be sensitive to UV rays, the components of black powder are not subject to "photodegradation." The brief exposure to sunlight as you pour a charge from your measure into the muzzle will have zero measurable effect on its chemical properties or performance.
The enemy is not the light itself. The enemy is what the light becomes.
2. The Real Danger: Light as Thermal Energy
From an engineering perspective, the problem is physics, not chemistry.
Black powder is black. Its color makes it an almost perfect absorber of the visible light spectrum. When light is absorbed, it is converted into heat.
This is the real danger.
Federal regulations for powder storage explicitly warn against this. The Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) in 27 CFR § 555.208 mandates that explosive materials be stored in magazines not exposed to "high temperatures or direct rays of the sun."
They are not worried about UV degradation. They are worried about thermal energy.
3. How Heat (from Light) Ruins Your Charge
Sunlight creates heat, and heat attacks your powder in two ways:
Safety Risk (Ignition): This is the most extreme risk. The auto-ignition temperature of black powder is approximately 801°F (427°C) (Source: GOEX Powder, SDS). While sunlight through a car window will not reach this temperature, it adds significant thermal energy to the system. A powder flask left in direct sun on a hot day can become dangerously hot, drastically lowering the threshold for ignition from another source, like a stray spark or friction.
Performance Killer (Moisture Cycles): This is the far more common problem for a shooter. A powder flask or horn left in the sun on your bench will heat up. Later, as the day cools, it cools down. This "hot/cold" thermal cycle causes the air inside the container to expand and contract. This "breathing" is what draws in microscopic, humid air from the outside.
This humidity is the #1 killer of black powder. The moisture dissolves the potassium nitrate, separating it from the charcoal and sulfur. This ruins the intimate mixture required for consistent ignition. The powder that was crisp and dry at 9 AM is now slightly "clumped" and slower by 3 PM. You are no longer shooting a consistent load.
Conclusion: Control the Variable
While the seconds of sunlight exposure during loading are irrelevant, the storage of your "ready" powder on the line is a critical variable.
In the Barrel: The charge is safe from light. This is not a concern.
On the Bench: Your powder flask or horn is at risk. Leaving it in direct sunlight is the same as leaving it on a heater. It will absorb thermal energy, leading to inconsistent performance via moisture cycling.
The Solution: Treat sunlight as a heat source. Keep your flask or horn in your shooting box, in a bag, or under a cloth in the shade. It's not superstition; it's controlling the thermal variable.
Tags: Black Powder, Engineering, Storage, Safety, Muzzleloader