The sniper rifle is the top-tier long-range weapon. It has a scope and deals much more damage than the hunting rifle, but has a very rare ammunition type and is a very fragile gun.
The sniper rifle has very noticeable sway to it when manually aimed. The sway can be reduced with either a higher skill level in small guns, or by entering sneak mode. At 100 points in small guns, the scope has no sway at all. However, a crippled arm will result in severe sway while using the scope, regardless of small guns skill level.
Even without Bloody Mess, sniper rifles can result in some fantastically gory kills, usually with the enemy's skull exploding. Weaker enemies frequently have several limbs blown off or are even reduced to mulch by a single shot.
A sound strategy to use with the sniper rifle is to be very stealthy and to have good knowledge of the area you are in. You will want to find a vantage point in which enemies either cannot reach or will take them a long time to reach you, usually some place high.
Manual aim is usually more accurate (especially at greater distances), but V.A.T.S. should not be overlooked. A head shot in V.A.T.S. that would normally take about a quarter of a high level enemy's health will, if unnoticed, instantly kill them, and for low level enemies, they will usually be very easily killed in just one head shot in any state. Be aware that your small guns skill should be max, and your rifle should be in good condition.
Victory rifle - While identical in strength to the sniper rifle, the Victory rifle has an additional 200 item HP, and knocks down targets with critical hits. However, it pays for this ability with a reduced critical chance of 3.
Reservist's rifle - Also identical to the sniper rifle in strength, the Reservist's rifle uses less AP to fire, but only holds 3 rounds in a magazine. It also fires slightly faster, and has slightly less recoil when using the scope.
Sim version Operation: Anchorage (add-on) - A sniper rifle with very high durability, which can be obtained through a glitch with the Operation: Anchorage add-on. See Operation: Anchorage glitches for details.
In the Bethesda Ruins, there is a raider with a sniper rifle west of the Offices West building very close to the spawn point. Every 72 in-game hours the raiders respawn. There is also a raider on the catwalk between the Offices East and Offices West buildings who carries a sniper rifle and has some ammunition nearby. He doesn't respawn.
On the bridge/overpass exactly north of Vault 101, south of Big Town, on the fourth or fifth raider from the beginning of the bridge. This raider also respawns every 72 hours.
Allistair Tenpenny of Tenpenny Tower. You can kill him while he's on the balcony of the top floor of his building or once he goes inside (you gain Karma for killing him but you are heavily advised to kill him outside, and if you kill the guard and the other people upstairs, no one downstairs will know you murdered them).
In the Point Lookout add-on after exiting the underground lab there is a smuggler carrying a sniper rifle and frag grenades on a small island south of where the Lone Wanderer climbs the ladder out of the lab. This smuggler respawns every 73 in-game hours.
pcps3xbox360 Outside V.A.T.S., with 100 small guns, the weapon can shoot as far as the game will draw non-player characters (playing at high resolutions will greatly improve non-player character visibility). However, the point of impact is higher than where the center of the scope is aimed. After the fire button is pressed, the scope aim will very rapidly jump up and shift slightly to the right almost at the same time the shot is actually fired. See the images below to determine how to compensate for this. [verified]
xbox360 Sometimes after fast traveling, only the lower sections of the rifle and the first lens of the scope will be visible. The top half and the rest of the scope will be invisible. To fix this, un-equip then re-equip the weapon. [verified]
The first two images above, taken from the southwest guard platform at Fort Bannister, will be a 1-shot kill. The color of the first shot has been inverted to improve clarity. The third picture shows how much aim compensation is needed for a head shot at very long ranges. It can be noted that the point of impact is always at the same length up along the vertical crosshair line above the center of the scope and slightly to the right.