To be honest, it is already common. The black dragons. And it is why it is always crowded. Also, you didn't mentioned to bring air strike runes or some magic runes so you will mostly hit the blk dragons first than anyone, since it is always crowded.
You also forgot to give credit for tipit when you grab their map details without their permission.
And getting a visage is very very very rare. And I'd rather kill iron dragons than blk dragons.
But for your effort in posting... I thank you I guess.
it can take up to 100s, 1000s, or maybe 10000s of kills. unless ur lucky enough to get it in less than 100 kills , which is very very very... very rare... just be sure to wield ring of wealth.