In essence M1918 BAR's meaner big brother with a prison record, the Gatling Gun is one of the best weapon assets in AHLCG. As it stands, I would say it's a game changer. My thoughts are in a few sections below:

Pros:

• Able to deal 6 damage in a single action, which is unrivalled across all weapon assets. A fair number of Elite enemies have 3 health, so these can be killed in a single action – tremendously valuable.
• Can have a staggering +6 on attacks, largely negating the need for other boosters or skills to commit.
• Starts with a good amount of uses. For example if just dealing two damage per action and so using two ammo, you could take 6 shots before needing to reload.
• Can kill groups of enemies, which is a massive boon for action economy.

Cons:

• When facing large groups of enemies (especially swarm enemies) the difficulty for the fight action can become very high.
• Failure on 6 ammo tests is punishing, as it wastes a lot of resources.
• If you're using multiple ammo on tests regularly, you need ammo support events in your deck.
• Sits in the class, and so is inaccessible for Guardians.
• The 5 resource price tag is on the costly side.

Deckbuilding Tips:

• Ammo support is almost certainly needed to keep you testing at high values. In this regard cards such as Contraband, Swift Reload and the off-class Extra Ammunition are all worth a mention. Contraband in particular doubles ammo on an asset.
• Tutoring cards can be beneficial to find it fast. Backpack •• does a deep deck search while also finding Supply ammo cards such as Contraband and Extra Ammunition. The off-class Prepared for the Worst is a good level 0 option for further tutoring. Underworld Market (even with the taboo) and Dirty Deeds present alternatives.
• Heavy Furs as well as the off-class Custom Modifications (EDIT: Strong-Armed doesn't work here) can all help against bag chaos bag pulls and so wasting large amounts of ammo.
• Cards such as Crack Shot which offer large boosts for when you're facing off against big groups of enemies can be useful.
• Healthy resource economy to afford the gun plus ammo support makes sense, such as Faustian Bargain, Bank Job, "Watch this!" and Easy Mark.
• Extra actions from Leo De Luca and Haste substantially increase damage output as long as you have enough ammo remaining.

Investigator Pairings:

• Tony Morgan was made for Gatling Gun. He has a of 5, is able to access Guardian cards such as Extra Ammunition and Prepared for the Worst, and often gains an extra action from Bounty Contracts.
• Michael McGlen similarly has a of 5 and "Viola" Case to find it, however you will need to manage Confiscation as this leads to Gatling Gun being reshuffled and so losing excess ammo. Friends in Low Places can be used to draw Confiscation early with a small gun in play and so get it discarded.
• Finn Edwards (depicted in the artwork) is a reasonable fit and he has Smuggled Goods as a tutor card for both the gun and support cards like Contraband. Dirty Fighting and Finn's free evade mean he can test at the same levels as Tony when the enemy is exhausted.
• "Skids" O'Toole has Guardian access and so can make use of many cards which work well with Gatling Gun, plus he can buy an extra action when needed.

Overall Gatling Gun is a very powerful card if properly supported, combining a massive boost with very high damage and the ability to kill groups of enemies like the Flamethrower. I'm not sure if it will remain un-tabooed for long, currently 5 XP is well worth the price of admission. I posted a Tony deck with Gatling Gun just before this review, so feel free to check it out for inspiration.