If you don't mine me critiquing your "bulge" ... when I turn a Sierra it looks basically like this one at the top but at the nib end I taper it down to the bushings with no bulge. I suppose the best way to describe it is to combine your original posted pen and this second pen.
What a great CA finish on it!! What grit do you sand to? CA only? Buffed? Micro-meshed?
Well, it's been a sort of experiment the last couple weeks. My first few pens I sanded to 400, then MM all the way to 12,000. Then I'd apply a little BLO on the bare wood, wipe it clean with a clean towel while spinning, apply some CA on a clean towel, wipe down the spinning pen. Then using the BLO towel, I apply a little more BLO to the pen and remove any excess. Repeat 5 times then sand with 600 to remove any ridges and go through the MM routine again.
This worked ok, however on some pens I started getting some kind of hazy foggy crap that wouldn't go away no matter how much buffing I did. This week I started trying it without BLO. Haven't had a problem since. The other things I changed were:
Sand to 400, stop lathe, sand with grain, start with CA. 5 coats, sand with 600, sand to 12,000, buff with carnuba. This has been a big improvement and no misses yet. However I do miss the chatoyance I got with BLO.