How can you shoot Armored Baron's mace?

[Loot Hunter]

The hint said that I should shoot the mace when it flashes green for the armor to turn off. But the green flash is like a fraction of a second. Am I supposed to have that kind of reaction?

[Hadjar]

yeah

[UNBREAKABLE]

You get used to knowing where you need to aim as he gets ready to cast that attack.

[Neo2266]

Don't pay attention to the flash, just start aiming when you see the wind-up animation. Ballista is the best weapon for the job.

Also you're better off turning the tutorials off completely and learning the mechanics by experience and from the codex entries.

[morbosfist]

Keep your eye on it and pop it with the rifle. It has to recharge after every attack, so once it's swung at you once, you can just wait for it to prep another.

[Strayfe]

The window for the attack is actually much longer than just the flash. Shooting his hand during any point where he slows down and does his attack animation will disable the armor. Hope this helps!

[Lunch]

Ballista, Precision Bolt, Sticky bombs, and Rockets will destroy the Baron's armor, try some of these.

[Dugaboo Windu]

Use the Ballista if you want. I find it's pretty quick hitting it's target.

[unrealization]

You can quite easily pop its armor using the Plasma Rifle's Microwave Mod without having to care for the flashing.

[Mortimer Reed]

If your reaction time and aim is not that good, you can also just blast his armor with the plasma rifle. The microwave mod is more effective but the regular fire also works. You don't have to shoot the mace if you don't want to.

[Loot Hunter]

Originally posted by unrealization:

You can quite easily pop its armor using the Plasma Rifle's Microwave Mod without having to care for the flashing.

Actually, that's what I do. But I'm too often run out of ammo for plasma.

Anyway, thank you all for advices.

[[RKB]Il Saggio]

The flash itself is a fraction of a second but the vulnerability window isn't. Similar to Marauders. They flash for a very short moment, but you don't need to time your counter attack that perfectly to catch them.
Also don't just react. You know he's gonna use his mace, so constantly keep an eye on it and the moment you see the attack animation start prepare your shot. Time window won't be an issue if you are prepared. Unless Marauders, who can be a bit random and there you can only react, Armored Barons are very reliable and easy to figure out.