@Epip Oc'Cabot On a new pipe, if you wipe the chamber out after smoking, with a paper towel/napkin, you’ll only build a 1mm layer of carbon, which is all you need, and you’ll never need a reamer.
If the carbon layer starts getting a little bumpy inside the chamber, after wiping it out, while it’s still warm, put a drop of water on a fingertip and gently rub it inside and you can make the carbon layer smooth/even.
Reamers are only needed if you don’t like to clean the chamber out after smoking, which is something you should do, or when buying an Estate pipe that has a thick cake in it.