Your statement is true.
Yeah, I've seen the tool as well but never known for sure if it was historic or of modern thinking although very logical. The trouble with doing it without a hardened liner is how it would respond to less material to erode in the barrel wall from heat and pressure.
Good points.
The trouble with that though is the internal cone bleeds off the main charge pressure needed for more complete combustion while also increasing flash hole ejection . Hardened stainless steel in the liner helps check the erosion but the flash hole exhaust is still markedly increased and becomes annoying to adjacent shooters.
It is true that the internal cone will mean a smoother flow of the pressure through the touch hole. The benefit of having powder closer to the heat from the pan ignition more than offsets the increase of gas through the touch hole. The internal cone is much larger than the touch hole and the ignition of that powder to the main charge is nearly instant rather that the short fuse effect of a long and tiny touch hole. There is only a very short time that the pressure from the ignition of the main charge is putting pressure through the touch hole.
The flash hole is exhausting hot gas the entire time the load is still burning in the barrel. The more gas that can be contained the more efficient the burn rate for velocity increase and less fouling. The internal cone only encourages the pressure exhaust where as the external cone can demonstrate the same effect by also shortening flash hole length and increase powder burn efficiency, without encouraging gas pressure loss. In other words external coning encourages pan flash inward rather than main charge pressure outward.
