Boomer

From Gears of War Realm - Gears of War Wiki Strategy Guide

The Boomer is a very large locust that carries the Boomshot weapon. On Hardcore and Insane, Boomers can and will kill you in one shot. Fortunately, they are extremely trigger-happy and when about to fire they will shout "Boom!" Listen for that and get your head down.

In terms of appearance, Boomers are effectively much larger and tougher versions of Grunts. They can take a disturbing amount of punishment (indeed, their main weakness is that they are such large targets. )They require a full two clips or more from the Lancer to kill - and the Gnasher tends to be surprisingly ineffective unless the Boomer is already badly wounded. They almost always travel in pairs and are dangerously effective when combined with Wretches.

Ways I have found effective for killing Boomers:

Longshot Rifle. It will take multiple headshots.

Boltok Revolver. Many headshots will be needed, and should be combined with the Lancer or the Gnasher.

Frag Grenade. A mere explosion will do little more than inconvenience a Boomer, but tagging one with it will gib them.

Boomshot. A highly effective way of taking down pairs of Boomers - especially in the escape from the Fenix estate - is to kill one with various other weapons and then use his weapon to kill other Boomers. If you can hit them directly it will gib them.

Torque Bow. The best anti-Boomer weapon there is, when you can find it. Easier to aim, more reliable, and you can carry a bit more ammo than the Boomshot.