The Great Bear Grenade Rifle is a unique Grenade Rifle that you can find in the location “Long 15”, after completing the Lonesome Road DLC with one of two specific endings.

Quick tips before you go get the gun:

• Incredibly difficult area. The location in which the gun is found is filled with some of the most powerful enemies in the game – heavily armored ghoulified NCR troops, who use heavy weapons and wear heavy armor. 
• Irradiated area. The entire area is heavily irradiated. Bring plenty of Rad-X and Rad Away. Do note that the radiation also makes the ghoul enemies regenerate HP.
• Lonesome Road DLC required. To get this weapon, you must have the Lonesome Road DLC installed.

Acquisition

First, you’ll have to make sure that you get one of two endings at the end of the Lonesome Road DLC. In this case, you’ll need to get either ending #1 or ending #3 from our Lonesome Road Ending guide (link to the guide can be found here).

Once you have that done, you can proceed to the Long 15. The entrance to the Long 15 can be found inside the Mojave Outpost.

Once there, you’ll find yourself standing on a destroyed road. Follow the road until you reach a destroyed NCR truck, then turn left. Be wary of all of the enemies here.

Walk between the destroyed truck and a crater. Keep going in that same direction, through a chainlink gate, until you reach a crashed vertibird.

Walk around the destroyed house you see in front of you and walk forward until you reach another crashed vertibird near what used to be a medical tent.

From here, go southwest. You’ll soon see a gun case that contains the weapon.

Comparing The Great Bear Grenade Rifle to the Grenade Rifle

• Deals the highest impact damage of all of the Grenade Rifle variants (15 damage vs 2 damage).
• Costs fewer AP to fire in VATS (32 AP to fire vs 35 AP to fire).
• Has the lowest spread of all of the Grenade Rifle variants (0.5 spread vs 1 spread).
• Has the highest durability of all of the Grenade Rifle variants (1245 shots before breaking vs 495 shots before breaking).

Gameplay Tips

• Due to its single-shot nature, the weapon is most likely going to be outclassed by the weapons that you’ll need to acquire this weapon, making it more of a collector’s item. For a point of reference, the non-unique Grenade Launcher outclasses this weapon in almost every category.
• Its higher accuracy is almost matched by that of the Thump-Thump from the base game, which also has more range and a large area of effect. Guide to acquire that weapon here.