The M40A1 Sniper Rifle is a weapon used by the HECU Snipers in Half-Life and the male Black Ops in Half-Life: Opposing Force. It is a powerful rifle that can kill many types of living beings in a single hit. It has a scope attached to it to make long range engagements easier. First introduced in Half-Life, the rifle model name was given in Opposing Force.
The M40A1 is first introduced near the end of the Half-Life chapter On A Rail in Sector E Materials Transport, right before the High Altitude Launch Center. In the chapter Surface Tension, two Snipers are spread around the Ordinance Storage Facility in the Topside Motorpool, and have shot a security guard who dies when Freeman reaches him. They add to the threat that the Land Mines and the Tripmines spread around the building already pose. The fourth and last HECU Sniper to be seen is found in the next map, in the same chapter, hiding in a window beside the barracks.
With this rifle, the HECU Sniper is able to drain a player's health in only a few hits, assuming the player also has no armor. The damage they do is decreased in the Source port.
In Black Mesa, it is found in the chapter Foxtrot Uniform. If not picked up there, it can be picked up from a dead male Black Ops in the chapter "The Package".
The M40A1 is a bolt-action rifle, resulting in slower firing speed, much slower than that of the Crossbow. To compensate for this, the M40A1's bullet will instantly hit a target with it's infinitely high projectile velocity. It also has perfect accuracy, no matter what the player is doing when it is fired.
For the tactics related to Half-Life, see the HECU Sniper article.
The M40A1 is best used to kill enemies in one shot from long range. One should try to pick off strong targets, such as Shock Troopers, that would otherwise take a lot of ammo and time to kill at close range.
In Hard mode, some strong enemies that used to take one bodyshot before dying (such as Shock Troopers) now take two. However, headshots can still kill those targets in one hit.
There is little ammo for this weapon throughout the game, so targets should be selected wisely.
If an enemy takes more than one shot from this weapon to be killed, one should simply take one shot at the enemy, then switch to the Desert Eagle or the M249 and finish it off. This preserves M40A1 ammo, which can be very helpful for later on.
In Deathmatch and easier difficulties one can use the M40A1 unscoped to kill single enemies just as well as the shotgun due to its perfect accuracy and high power.
An easier way to take down the Gene Worm is to disable the eyes with the mounted guns then fire a single shot into the portal in its stomach (the void behind the portal is the vulnerable area). This can greatly accelerate the fight.
Behind the scenes
Killing the HECU Sniper, consisting of a human shooting target using the "func_breakable" entity, makes both the rifle and the silhouette brushes disappear. The rifle itself is a brush using the entity "func_tank", not affected by the console code "notarget".
In Opposing Force, the Sniper Rifle originally had a different scope with a variable zoom, as well as different animations.
Only one Black Ops Male Assassin is seen using the M40A1 in Half-Life: Opposing Force, during the chapter Foxtrot Uniform.
When used by the Black Ops Male Assassin, the M40A1 is reloaded after each shot, and only does 15 points of damage per hit. This is solely for balance, as it would be very difficult and frustrating to navigate through that part without getting hit.
In Half-Life, HECU snipers use the M40A1 in semi-automatic mode rather than bolt-action, and deal low damage against Gordon.