You've made nice pens! I have a couple of suggestions about the design:
1. Shorten the cap threads - a lot. Based on the feedback I got from fountain pen collectors/afficionados/users, I aim for between 1 and 2 full turns of the cap to go from "off" to "fully seated".
2. Eliminate the space where you turned away the threads next to the barrel. If you did it because the cap won't screw on all the way (because the threads aren't fully formed in that last millimetre or two), solve the problem by paring away the threads inside the cap (where it's out of sight) rather than having it out in the open.
3. I use fountain pens every day (at least two, loaded with different coloured ink), and have developed an attitude about pen barrels that step down into the cap-threads & nib section. If it's rounded, I can live with it, but a sharp step irritates my thumb and/or finger while I'm writing. My preference is for the cap to be proud of the body, and the body smooth from the nib all the way to the closed end. But that's just me, I know others feel differently about it and rave over a seamless cap & barrel.
As I said - your execution looks to be top-notch, they polished up beautifully. (Did you buff them after sanding?) I look forward to seeing more of your pens.