Before I pursue this line of thinking I'm curious if anyone else already has and what the results were. Weeks ago I pulled one of the nozzles of my creator pro because it kept scraping ever so slightly on my prints and causing problems with certain geometries. In doing so I realized what should have always been obvious, the ptfe liner is cut off square but the hole in the feed side of the nozzle is tapered due to the shape of the drill that was used to bore it. The result is that as the filament is pushed into the nozzle, there is an area where it is no longer guided by the liner but not yet being extruded. Plastic has to fill this area up before it will consistently exit the nozzle. During printing that doesn't seem like it would be a problem but when the carriage is moving without printing (or when the other nozzle is being used) that leaves a reservoir of molten plastic that can ooze out and ruin prints. Retraction only helps so much because you're never going to pull out that molten reservoir of material (as evidenced by the need to purge when changing filaments). So my thought is that if the shape of the liner and the interior of the nozzle were more closely matched, that reservoir could be eliminated or at least reduced resulting in less plastic sitting around waiting to drip out.

So then it seems there are two options to look into
1) bevel the end of the liner to match the angle in the nozzle, this would allow the liner to seat further down in the nozzle. Cheapest and easiest option to test but would be a pain in the ass to do regularly without some sort of bevelling fixture
2) bore the nozzles with an end mill or similar to remove the drill point chamfer. More expensive up front because it requires a new nozzle to be custom made but it means that future liner replacements need only be cut off square as is the current practice.

Thoughts or experiences?