By Duane Thomas
In the first four parts of this five-part series on the components of priming compounds, we discussed the initiator which is stored energy, the sensitizer which places the initiator in a more-excited state thus makes it more likely to detonate when exposed to impact energy, the frictionator which creates little micro-hotspots in the priming compound when crushed, and the oxidizer which supplies oxygen to nourish the flame. Now let’s address the final component, the fuel.
The “fuel,” as the term in used for priming compounds, is the primary burning material. This is what everything else, the initiator, the sensitizer, the frictionator, the oxidizer, is there to make it burn. Common fuels are antimony sulfide, and aluminum.
Antimony sulfide not only acts as a fuel, but due to its crystalline structure also acts as a frictionator (as discussed in Part 3). About the only bad thing we can say about antimony sulfide is that antimony is a heavy metal, so we really don’t want to be taking big, hefty snorts of the stuff on a regular basis.
Finely powdered aluminum, as it burns, consumes oxygen released by the oxidizer, and as a result produces aluminum oxide, therefore intense heat and flame. Because aluminum is not a heavy metal (both actual weight-wise and periodic table-wise), we see it a lot in lead-free primers, but it’s also used in Federal centerfire primers.
So, we put it all together at the end, when priming compound ignites, the initiator (usually lead styphnate) detonates under impact, its tendency to do so amplified by the sensitizer (usually tetrazene) and the frictionator (usually ground glass), while the oxidizer (usually barium nitrate) supplies oxygen which feeds the fuel (usually antimony sulfide) which burns. This produces a hot flame and shockwave that flows through the cartridge casing’s flash hole, into the interior of the cartridge casing, and ignites the gunpowder contained within.
