I am talking about shooting flintlocks not train engines. It doesn't seem many know what a "Klinker" is. Or how to fix one.
Please tell us more.
Since bluenoser asked.
As we shoot the fouling builds up down in the breech of our barrels until it's quite thick. Weather conditions can make this worse on certain occasions. The more we shoot the worse it gets until the coating below the touchhole breaks loose and becomes like a slab that now can move. When this "slab" of fouling moves up and covers the TH from the inside it becomes known as a "Klinker".
That is entirely possible Pukka, that is the time frame when they were most prevalent. But rarely they can still occur.
When this has occured to me I've taken a pick and tried to move it so I can get fire to the charge. If your TH is big enough you can see it as a gray slab blocking the TH. If I can't move it I take a pick with a point on the end and dig into it until I get enough of a hole to shoot the gun. Often the gun is loaded before you become aware of it.
The "Klinker" is a main reason for the practice of loading a gun with a pick in the TH.
I've only experienced this at home during long shooting sessions without cleaning the rifle. So to prevent them I clean the rifle regularly. Often I plug the TH with a toothpick, then pour a little water down the barrel and let it sit while I do something else. Then I turn the rifle TH up, remove the toothpick and place a wadded up paper towel in the pan and close the frizzen. Next I insert the ramrod slowly a little more than halfway down. Turn the rifle bore up and with a sharp press of the RR blow the fouling out the TH and into the paper towel. I do this a couple of times until no more fouling comes out. Then run a wet patch down the barrel to clean the grooves then back to shooting.
As long as I clean the chamber area regularly I get no "Klinkers". I had rather try to prevent one than fix one after the fact.