The Percussion System, Part 2: The "Engine" Re-Engineered
In our last post, we defined the percussion system as a revolution. It replaced the flintlock's 80ms, open-pan ignition with a ~25ms sealed-cap ignition.
This was achieved by engineering a simpler lock. The percussion lock is a case study in removing components. The frizzen, the frizzen spring, and the flint-holding "cock" are all gone. The lock's only job is to provide a single, forceful, downward strike.
However, this "simpler" system introduces new, critical variables. The flintlock required balance; the percussion lock requires brute-force management.
1. The New Mechanics: Hammer vs. Cock
A flintlock has a "cock," named for its shape, which holds a tool (the flint). A percussion lock has a "hammer." Its job is not to hold a tool, but to be the tool. It is a mass of metal designed to transfer kinetic energy.
The engineering challenge is to deliver the exact right amount of energy. This reveals the two primary failure modes of the percussion engine:
Failure Mode 1: Insufficient Force (Misfire) If the mainspring is too weak or the hammer is too light, the hammer falls but does not have enough energy to crush the fulminate primer. This results in a "dented cap" but no ignition. This can also be caused by "hammer bounce," where a poorly-tuned lock rebounds fractionally at the bottom of its arc, failing to deliver its full impulse blow.
Failure Mode 2: Excessive Force (Cap Splitting) This is a far more common and dangerous failure. If the mainspring is too strong or the hammer face has an improper "fit" to the cap, the hammer strikes with so muchforce that it splits the copper cap apart.
When a cap splits, two things happen, both of them bad:
Gas Venting: The path of least resistance is no longer down the nipple. The hot ignition gas blows out the side of the split cap. This vents pressure that should be igniting the charge, resulting in a slow, erratic "hangfire."
Shrapnel: It sends hot, frangible pieces of the copper cap flying, often directly back toward the shooter's face.
The Engineering Fix: A properly engineered system matches the hammer face, hammer mass, and mainspring strength. The hammer face should be cupped to perfectly envelop the cap upon striking, containing the blast and preventing it from splitting.
2. The Achilles' Heel: Internal Fouling
The percussion lock's greatest strength—its "closed" system—is also its greatest mechanical weakness.
A flintlock fouls externally. The pan flash is messy, but it happens on the outside of the lock plate.
A percussion lock fouls internally.
The Physics: When the hammer crushes the cap, the fulminate explodes. This creates a small, violent blast of hot, corrosive gas. That gas travels in two directions:
Forward: Down the nipple's flash channel to ignite the main charge (the intended path).
Backward: Back out from under the cap's skirt and through the nipple's threads.
This "blowback" is the system's fatal flaw. This gas, a mix of fulminate residue (mercuric) and potassium chlorate (from the cap) and black powder residue (sulfur), is intensely corrosive. This "primer-fouling" is, as documented by virtually all ordnance manuals and NMLRA publications, one of the most rust-inducing substances in firearms history.
This corrosive gas is blown directly into the precision-tuned internal parts of your lock—the tumbler, the sear, the mainspring.
Conclusion
The percussion lock is a trade-off. We traded the external unreliability of a flintlock (humidity in the pan) for the internal unreliability of a percussion lock (corrosion).
We solved the "lock time" problem but created a "maintenance" problem. While the flintlock shooter's enemy is the weather, the percussion shooter's enemy is rust.
This means that while the lock itself is a simple "hammer," the component it strikes is not. The "nipple" is the most critical and highest-wear part of the entire system.
In our next post, we will analyze the "nozzle" of this new system: the nipple and its flash channel.
Tags: Percussion, Engineering, Lock Tuning, Nipple, Muzzleloader