Easiest way I've found to keep the airway clear is to leave the drill bit/mandrel/etc in the coil until you're finished with the build, then gently twist the bit out. You may still get a bit in the way of the air hole, but for the most part it stays clear all the way thru.
-Kingboomer
ETA: Not sure if you know this trick, but here's how I get the heads appart (not me doing the vid):
https://www.youtube.com/watch?v=nuvA65u6T-Y
This works for both BVC and BDC
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