How Does a Touch Hole Liner Improve Reliability?

[smoothshooter]

In answer to your question, they don't necessarily ! Keep in mind flash hole liners for the average flint gun is a modern notion as virtually all of the originals we settled America with never started life with flash hole liners. They were most often employed for repairs when flash holes became eroded from hard usage or cleaning neglect.

Your statement is true.
However, some barrels left their maker with an enlargement done from the inside to shorten ignition time.
I have seen one picture and 2 very detailed drawings from the mid to late 1700’s showing the tool this operation was done with. A very complicated tool for the times.
I think the inside-coned vent hole feature started out as more of a British thing done on some higher quality guns.

 

[smoothshooter]

Your statement is true.
However, some barrels left their maker with an enlargement done from the inside to shorten ignition time.
I have seen one picture and 2 very detailed drawings from the mid to late 1700’s showing the tool this operation was done with. A very complicated tool for the times.
I think the inside-coned vent hole feature started out as more of a British thing done on some higher quality guns.

 

[M. De Land]

Your statement is true.
However, some barrels left their maker with an enlargement done from the inside to shorten ignition time.
I have seen one picture and 2 very detailed drawings from the mid to late 1700’s showing the tool this operation was done with. A very complicated tool for the times.
I think the inside-coned vent hole feature started out as more of a British thing done on some higher quality guns.

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.
It certainly was known about as high end European arms are often lined with platinum and gold rivet/linings. The interior coning tool makes me wonder if this wasn't really made for the gold and platinum rivet lining installations instead of coning flash holes . The interior coning certainly does encourage main charge pressure escapement and probably faster hole erosion.

 

[smoothshooter]

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.
It certainly was known about as high end European arms are often lined with platinum and gold rivet/linings. The interior coning tool makes me wonder if this wasn't really made for the gold and platinum rivet lining installations instead of coning flash holes . The interior coning certainly does encourage main charge pressure escapement and probably faster hole erosion.

Good points.

 

[M. De Land]

Relief of the touch hole entry does improve the flow of heat from the pan through the touch hole. The heated air can be thought of as a fluid. When a fluid encounters sharp corners, turbulence develops disrupting the efficient transfer of heat to the powder charge. It only takes a little bit of relief to improve fluid flow. With an internal cone, that powder is no longer a fuse but by being many times larger than the touch hole, that powder is a part of the main charge.

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.

 

[AAAPAUL]

Use a vent pick every time you load and it will speed up ignition too

 

[Grenadier1758]

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.

I have attached a flash guard to the pan to deflect the jet of gas from the ignition of the main charge away from adjacent shooters.

 

[M. De Land]

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.

I have attached a flash guard to the pan to deflect the jet of gas from the ignition of the main charge away from adjacent shooters.

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.