When I make liners, I just buy a stainless steel threaded rod...
I countersink the end that will be on the inside and screw into the barrel...I then cut, leaving about 2-3 threads so I don't scratch the barrel and file flush with the barrel...I then drill the touchhole with the bottom of the hole just above the top of the pan, so the hole is covered by the frizzen when shut...

By countersinking the inside, the powder in the barrel is about a 1/16th of an inch away from the outer wall of the barrel...The touchhole can also be drilled off center if needed...Many production guns have the touchhole too low and it gets plugged with powder...