This weapon was originally a U.S. checkpoint guard carbine used in Canada, issued from the Long Branch Arsenal in Ontario, USA territory. Chambered with the 12.7mm round, this rifle was supposed to offer guards the firepower necessary to intercept anyone attempting to breach a checkpoint, regardless of equipment.
This particular rifle once belonged to Randall Clark, an ex-U.S. army serviceman who found himself hiding out in Zion National Park after the Great War. The rifle was used by the Survivalist for decades and shows signs of improvised repair such as clamps on the foregrip wood itself made of mismatched wood furniture. The front sight is also damaged. Clark apparently couldn't repair it, using it as-is.
In terms of in-game performance, the rifle has a very decent rate of fire, relatively low spread, respectable AP cost, and a high damage that can be raised considerably with Grunt; the damage is slightly higher than This Machine loaded with regular .308 rounds if Grunt is taken, but the Survivalist's rifle shoots faster and far more accurately. Even if This Machine is loaded with .308 JSPs, the damage difference isn't substantial and can be mitigated by using 12.7 JHPs from the Gun Runners' Arsenal add-on.
However, it uses rare 12.7mm rounds that generally must be bought from vendors, and the high rate of fire makes it relatively easy to waste ammunition if not careful. The spread is high enough where a scoped rifle may be a better option for very long ranges. The bent iron-sights, which can be rectified (see the notes below), may require a bit of practice if using true iron sights.
The Survivalist's rifle can fire a total of about 2495 standard rounds, the equivalent of 250 reloads, from full condition before breaking.
When looking through the iron sights to aim, the forward sight is bent out of line with the rear channel on top of the carrying handle, thus not creating the sight picture seen when using an undamaged service rifle. However, using the upper right side of the bent front sight as your aiming point corrects this, providing a usable, (albeit confusing), solution to this problem.
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. Long Branch is actually found in the southwest end of Toronto, Ontario. Historically during WWI and WWII a small area further west of Long Branch known as Port Credit manufactured rifles used by the Canadian forces during the wars.
Nearby NPCs or your companions may take the rifle from the bag that it appears in.
If you complete Honest Hearts before retrieving the rifle, and a non-player character has picked up the rifle you will not be able to acquire the rifle because all non-player characters besides enemies disappear from Zion upon completion of the add-on.
Compared to the standard variant, the barrel of the rifle is shorter in length, but wider in diameter. This is a correct real world characteristic, as the 12.7mm is more than double the diameter measure of the 5.56mm round, and the 12.7mm has a higher pressure measure than the 5.56mm, and most likely a longer casing then the 5.56mm round. The shorter length can be attributed to the fact that it is called a carbine while the service rifle is not a carbine.
Behind the scenes
The French word "Arrêt", translated as the words "stop" or "halt", on one side of the stock is paired with "Stop" written in English on the other side of the rifle's stock. This, combined with information from Randall Clark's terminal entries, indicates that this rifle was used during the U.S. occupation of a bilingual area of Canada. However, the way it is written on the rifle is in noun form so it would be closer to "a stop" (e.g. a bus stop) as found on stop signs in French.
The Survivalist's rifle was loosely based on the .50 Beowulf AR-15 platform conversion.