The Inline Revolution, Part 1: Solving the Sidelock's 90-Degree Problem
In our last series, we engineered the percussion sidelock to its mechanical limit. We were left with two fundamental, system-level flaws:
The "Plumbing" Flaw (Part 5): The 90-degree drum/bolster is a fluid-dynamics nightmare. It’s a "fouling trap" that causes misfires.
The "Fuel" Flaw (Part 6): The percussion cap lacks the thermal energy to reliably ignite modern, high-performance (and high-ignition-temperature) black powder substitutes.
The sidelock, like the flintlock, had hit its engineering ceiling. The solution was not an evolution; it was a revolution.
This revolution was the inline muzzleloader.
The New Architecture: Straight-Line Ignition
The inline rifle, perfected by Tony Knight with his MK-85 in 1985, is defined by its new architecture. As the name implies, the ignition, propellant, and projectile are all "in a line," or co-axial. (Source: American Hunter, "The Return of Knight Rifles").
This single design change solved the sidelock's worst flaw.
The Problem: The sidelock's 90-degree drum.
The Solution: A removable, co-axial breech plug.
By placing the ignition source directly behind the powder, the inline system creates a perfectly straight flash channel. This is the "perfect" straight-line path we theorized in our percussion series. It is the most efficient, unobstructed path for the ignition flame to travel. There are no 90-degree corners to trap fouling.
The New Fuel: The 209 Primer
This new architecture was paired with a new "fuel" source. The inline system abandoned the #11 percussion cap and adopted the 209 shotshell primer.
This was the real genius of the system. The 209 primer is not just a cap; it's a furnace.
Engineering Comparison: Ignition Energy
#11 Percussion Cap: A small cup of primer designed to be just hot enough to ignite real black powder.
209 Primer: A self-contained primer/anvil system designed to ignite modern, slow-burning smokeless shotgun powder. It produces a "much hotter spark" with a significantly greater flame volume and duration. (Source: Hunter-Ed.com).
The System-Wide Solution
The 209 primer and the inline breech plug are an engineered system that solves all of the percussion lock's problems at once.
It Unlocked New Propellants. As we've established, substitutes like Pyrodex have a higher ignition temperature than black powder. (Source: American Longrifles). Modern propellants like Blackhorn 209 are so hard to ignite that the manufacturer explicitly states they will not work with #11 caps and require a hot, standard 209 primer. (Source: Blackhorn 209). The 209's furnace-like blast easily and reliably ignites these modern propellants, including pellets.
It Solved Blowback. The inline's bolt-action or break-action creates a sealed breech. This contains the 209's powerful blast, stopping the corrosive blowback that plagues sidelocks. This prevents gas from escaping, directs 100% of the ignition energy forward, and keeps the "engine" (the firing pin/bolt) clean. (Source: Guns.com, "The Rise of the Inline").
Conclusion
The inline rifle is the pinnacle of muzzleloading engineering. It is a sealed, straight-line ignition system that pairs a high-heat "detonator" (the 209 primer) with a fouling-resistant "plumbing" (the breech plug).
This new system is what allowed muzzleloading to evolve from a 100-yard "whoosh-bang" into a 200-yard, high-velocity sport. In our next post, we will analyze the "engine" of this new system: the breech plug and its different designs.
Tags: Inline, 209 Primer, Engineering, Tony Knight, Muzzleloader