This weapon was originally a U.S. checkpoint guard carbine in Canada, issued from the Long Branch Arsenal in Ontario (former Canada). Built to use the 12.7mm round, this rifle was supposed to offer guards firepower necessary to intercept anyone attempting to breach a checkpoint, regardless of equipment.
The one found in Zion once belonged to the Survivalist, an ex-U.S. army serviceman who found himself hiding out in Zion National Park after the Great War. The Survivalist's Rifle was used by the Survivalist for decades and shows signs of improvised repair such as clamps on the foregrip wood, the mismatched wood furniture, etc. The bent front sight is damage that the Survivalist couldn't or didn't repair and just adapted to using as-is. 
When looking through iron sights to aim, the forward sight is bent and out of line with the rear channel on top of the carrying handle, thus not creating the proper sight picture as seen when using a normal service rifle variant. However, using the upper right side of the canted front sight as your aiming point corrects this problem and providing a useful (albeit confusing) solution to this design feature. Alternatively, you can opt to turn off true iron sights, which bypasses the sight issue.
Even when visiting before anything else, there still may be hostiles. (Cazadors, White Legs, etc.)
- Sometimes when killing a human enemy with a torso shot, the Survivalist's Rifle will cause their body to travel a fair distance.
- "Arrêt" is a French word for "stop" or "halt".
- A star in a circle similar to that seen on the US flag is seen above the magazine on the rifle's right side, along with the words: "PROPERTY OF U.S. GOVT CHKPNT CARBINE 12.7MM CAL".
- Above the trigger the words "LONG BRANCH ARSENAL ONTARIO, USA TERRITORY" are present.
- Xbox 360 The rifle may not appear in the duffel bag at all. However, it's possible that a nearby enemy picked the weapon up. It may appear on an NPC, it has been found in Walking-Clouds inventory without it having been previously found.
- PC During the Advanced Scouts quest for Daniel, a White Legs tribe member may take this weapon from the sack. Be sure to check all bodies.
- Sometimes when using hollow point ammo and getting a critical hit this weapon will do 1000+ damage.[verification overdue]