If you want to checker the solder at the end of the tubes it is very easy to do. all you need is a cork to lightly plug the barrel and a quality set of dividers to scribe the lines in the solder. Simply put one end of the divider in the center of the cork and visually space the lines. It is not deep so don't push to hard. Change the setup to the second barrel and make the cross hatch pattern.
bill