By Duane Thomas
In the first two parts of this five-part series on the components of priming compounds, we discussed the initiator which is stored energy, and the sensitizer which places the initiator in a more-excited state thus makes it more likely to detonate when exposed to impact energy. Now let’s address the frictionator. Which is surely the coolest of the five terms, but what actually does it mean?
The classic frictionator added to priming compound is ground glass. This increases the sensitivity (i.e. makes the priming compound more shock-sensitive, more likely to detonate when struck) by adding abrasive particles to the mixture; these generate heat through friction when the compound is crushed. Frictionators are most-commonly used in rimfire priming compound because there’s no anvil to focus the impact energy, and still used, but less invariably so, in many centerfire primers.
How ground glass enhances ignition-reliability in priming compounds is by creating, essentially, little micro-hotspots during compression. This lowers the energy needed to detonate the sensitizer which in turn detonates the initiator. There are other frictionators in use besides ground glass, but ground glass is the go-to due to its effectiveness and low cost.
The frictionator, or lack thereof, can also influence the combustion profile, i.e. how the powder burns, and how it exits the flash hole. With a frictionator, the primer produces a more directed, high-velocity “jet of flame” due to the intense, localized heat and pressure from abrasive ignition. Federal centerfire primers famously do not contain ground glass thus they tend to produce more a “ball of flame” than a “jet of flame.”
Because the frictionator amplifies the pressure wave produced by the primer, the flame produced tends to exit the flash hole as a high-intensity, comparatively narrow “jet of flame.” This causes it to penetrate deeply into the propellant bed (the gunpowder inside the casing). Essentially, the flash hole acts as a focusing nozzle.
In the absence of a frictionator in Federal centerfire primers, the priming compound relies instead for ignition sensitivity on having a higher tetrazene content (which we discussed during “Part 2: The Sensitizer”) and a finely tuned oxidizer/fuel mix (which we will discuss in Parts 4 and 5). Without the abrasive friction of glass, combustion is less localized, and more uniform, across the priming compound. In essence, primers without a frictionator are more low-pressure, therefore instead of a “jet of flame” they produce more a “ball of flame” where the flame spreads out and saturates the gunpowder instead of driving deeply into it. The fact that Federal primers have a higher tetrazene content and rely for their sensitivity on the chemical composition of the priming compound instead of adding a frictionator then compensating for the frictionator by going for a less-sensitive initiator/sensitizer mix, is one huge reason Federal primers are famously “sensitive.”
