Started leveling a Sentinel for Forge Guard summoner in Multiplayer. First time using MultiStrike, I have leveled it to level 7. I went right for ASPD 2/3. North for Perfect Steel, East for both Doctrine of the Anvil & Firey Justice.
This puts the skill at a maximum of five armament stacks, and then casts Forge Strike.
I find while moving along, if I start stutter-step-attacking (Right-Click an enemy, click to move, Right-click an enemy), MultiStrike will drop armament stacks.
You can visually watch the skill timer for stacks that should drop. When you auto attack, the stack number will increase, and the cooldown timer will reset to max, but if you time it correctly you with a slower step-attack-step the stack will drop by one. It is as if the visual CD timer is not synced to the actual stacks, nor is actually being reset and asynchronous of the visual stack timer.
I can hold down right-click and stacks will count accordingly to the maximum and then proc the forge strike correctly. This leaves no ability to time my attacks to place forge strike where I want though.