Ryan Grizzle (OWB Holsters - R Grizzle Leather
) reinforces the mouth with an extra layer of leather. Others sew in a steel band, but mostly for IWB holsters. I have several revolver holsters by Alessi, which aren't reinforced but asymmetrical. As described above, a little twist with finger pressure on one of the lips gets the job done.
Mostly it takes practice. You have to spread the opening enough to clear the cylinder. Sometimes it works best to have your index finger alongside the cylinder to push the lip aside, and your thumb on the hammer for safety (and leverage).
Alessi holsters (CQB and Belt Slide) cover the recoil shield. To draw smoothly, I pry a bit with my thumb and pull somewhat outward on the grip. Again, practice.