A common problem with the Ameroclassic pen, and similar kits, is that of the wood on the bottom barrel binding inside the cap ring. If the wood is larger than the collar at the top of the lower barrel, or have any eccentricity with it, there will be the possibility that the cap will be too tight to turn easily.
I always cut a relief about 1/16" long and down to the bushing diameter at the top end of the lower barrel. That allows me to make the lower barrel a larger diameter without binding inside the cap.