Gears of War made its way into Wasteland 3 with an assault rifle that is fairly good all-around but not necessarily the best in all situations. This guide should lead you straight to it.
Lancer, the legendary assault rifle Cogs tend to use, has made its way to Wasteland 3, undoubtedly as a result of Microsoft acquiring inXile Entertainment during the game's development.
Anyway, the rifle can be found in the southernmost parts of the map, meaning you will have to upgrade your Kodiak's radiation resistance to level 3. You can either get the Dominator Chassis at the garage vendor in Ranger HQ or the Rad Shields utility item in the building while attempting to save Morningstar.
Lancer can be obtained late into the game when you are already on the way to deal with Liberty. When you reach Yuma county, head west and hug the southern border of the map until you reach the correct location, at which point you will be prompted by the game to decide what to do during the "Mysterious Wreckage" encounter. The exact location of the rifle can be seen on the map below.
The encounter itself has no skill checks and you can loot the weapon with no investment other than 10 in Automatic Weapons because that's what the gun requires.
As for the stats, it actually deals less damage than Socom Assault Rifle to organics and less than Atom Smasher to synthetics. On the other hand, the weapon seems to be a combination of great things from both worlds since it doesn't have the -30% penalties Atom Smasher does and has enough armour penetration to go through any protection in the game.
This makes it the perfect candidate for the rare Quickfire Mag if you are looking for a great all-around weapon since you won't need to upgrade two rifles and can just go to town with those 3AP bursts on any enemy you see.