As some of you have figured out, this is happening regardless of weapon or profession because the achievement only progresses when you make the killing blow with a weapon skill. If you do not make the killing blow with a weapon skill, or if the "killing blow" comes from a condition, the achievement does not progress.
We're working on a change that will progress this achievement as long as you deal any damage with the relevant weapon. Achievement progress will be granted for the weapon(s) you are wielding when the enemy dies.
We need to test this extensively across all professions to make sure that nothing causes players to lose achievement progress they have already earned, so we are planning for this to ship with the March 19 systems update.
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