I recently got quite a few nibs from a 'nib technician', various #6s including a medium and broad stub, a smoothed out fine, and a couple of other bits.

These are JoWo nibs, but I wanted to put them on pens with Bock nibs and feeds. They fit on there just fine, I made sure tines were aligned, etc., but not one of them felt good when writing. I've tried the 3 different JoWo nibs on 2 different pens with Bock feeds and they just don't seem right - in no way can I describe any of them as smooth (though not exactly scratchy), and the writing experience feels sort of inconsistent (not ink flow, just the character of the nib is constantly changing as you write).

The nib does not move on the feed and seats in the nib unit happily. Ink is happily gushing forth.

Does anyone have any experience of this? I've done it in the past with a certain pen I no longer own with no problems, but that was a few years back... Wondering if the slightly different feed shape is pushing something out somewhere.