Speaking of mistakes, which Nathan brought up. On my current build, a Fainot fowling piece, I was pretty sure I did the drilling for ramrod thimbles perfectly. I used just 1 pin on upper thimbles because it looks like that is how Fainot did it. But then a couple weeks later I noted a couple of them were a little wiggly. Not happy. I never like to plug and re-drill. Sometimes it has to be done but it bugs me.
To fix the problem I took a leftover piece of stock wood about half an inch wide and set my best plane for a thin shaving. I then ironed those curly shaving flat with a steam iron. Then I cut to length and width with scissors and glued them into place in the thimble inlets, inserting and clamping down a dowel wrapped in soda bottle plastic to squish it good until the glue set overnight. Worked like a charm and looks good too. But from now on I may use 2 pins for all thimbles whether the original builder seems to have done so or not.