From TF2 Wiki
The Sentry gun (sometimes known as a "Turret", "Sentry" or abbreviated to "SG") is a building that can be constructed by an Engineer and functions as an automated weapons platform that fires upon any enemy who enters its line of sight. The Sentry Gun will always target and fire on the closest enemy player or building, provided they are within firing range and in line of sight of the Sentry (not behind a wall, etc).
The Sentry gun costs 130 Metal to build, 200 Metal to upgrade to level two, and an additional 200 to upgrade to the third and final level. With each upgrade level the Sentry gun becomes more powerful, gaining machine guns, rockets and the ability to take more damage. The firing range remains constant regardless of level.
The Sentry gun's ammo may be replenished with your own metal by hitting it with your Wrench. Each bullet reloaded costs 1 metal and each rocket salvo costs 2 metal.
When placing a Sentry gun, the limit of its range is represented by a 3D sphere of your team color. A Sentry that is being constructed will have its health increase gradually until it reaches its maximum health upon completion. The Sentry rotates 90 degrees to patrol the area, but is capable of rotating 360 degrees to lock on to a target. This takes a brief moment however, which may allow faster foes to slip past its range. The Sentry can also be manually rotated to face a different direction before you build it: When the blueprint is shown, using the alternate fire button (default key: MOUSE2) will rotate the blueprints clockwise by 90 degrees.
Sentry guns will not fire upon enemy Spies that are cloaked or disguised. Sentry guns are unable to fire if an enemy Spy attaches an Electro sapper to it, if they are being upgraded/built, or if they're under the effects of the Cow Mangler's Alternate Fire. A destroyed Sentry gun leaves 60 Metal worth of pieces, which can also be picked up by other classes as Ammo.
Unlike most other weapons, the sentry gun's weapons do not get affected with damage falloff from range nor can it gain criticals. It is possible however, to make the Sentry gun deal Mini crit attacks and damage if its target is coated in Jarate or if the Engineer who built the sentry is close to a Soldier with an active Buff banner, boosting the damage of each bullet to 22.
All level sentry's can be picked up when fully deployed only. When the engineer carries his sentry or other building, he walks with the speed of a heavy and can not use any weapons. When he gets killed, his carried building gets instantly destroyed, which gives a kill icon of a engineer box with a explosion. A redeployed sentry automatically builds back to its previous level and builds 2 times faster then normal or more when hit by a Engineer's melee weapon. A redeployed sentry has no health at the start of the build, just like a normal sentry. Once it has been deployed and before it reaches the end of its Level 1 animation, the owner can use the Wrangler to put a shield around the sentry as it goes through its Level 2 and 3 animations. At the end of its build animation to the Level it originally was, it will automatically start firing at any nearby opponents or be Wrangled. Sapped buildings can not be redeployed.
Sentry Gun Levels
|150 (up to 450 with Wrangler)||130 Metal||Semi-Automatic Firing Barrel|| 14-18 damage
4 shots per second
64 average DPS
|180 (up to 540 with Wrangler)||330 Metal||Dual Rotational Minigun Barrels|| 14-18 damage
8 shots per second
128 average DPS
|216 (up to 648 with Wrangler)||530 Metal||
|100 (up to 450 with Wrangler)||100 Metal||Semi-Automatic Firing Barrel|| 7-9 damage
6 (12 with Wrangler) shots per second
48 (96 with Wrangler) average DPS
Combat Mini-Sentry Gun
The Combat Mini-Sentry Gun is a more offense-oriented version of the standard Sentry Gun, and is a component of the Engineer's Gunslinger unlock. The Combat Mini-Sentry Gun has several advantages: it costs only 100 metal to place, constructs at four times the speed of the original Sentry Gun, and is deployed at full health. However, it is neither repairable nor upgradable, as it is intended for short-term use rather than long-term area denial fortification. It also deals only 50% the damage of the original Level 1 Sentry Gun.
- The Engineer apparently designed and built the Sentry Gun under contract from 'TF Industries' in 1965.
- The official game manual for Team Fortress 2 is actually the Sentry Gun Operating Manual.
- Engineers can receive a "Sentry Gunner" achievement for racking up 10 kills with a single Sentry gun; the Engineer can die, as long as the Sentry Gun does not.
- A label on the Sentry Gun blueprint reads "Automatic Sentry Apparatus;" however, the Sentry gun manual refers to it as a "Sentry Mechanical Firing Device".
- Like all Buildings, Sentry guns can be built underwater.
- Sentry guns cannot fire through a Dispenser built by an Engineer of the same team.
- The Sentry gun makes a number of beeps every time it reverses its rotation. The number of beeps corresponds to its upgrade level, where a level 3 turret makes three quick beeps. Additionally, the higher the Sentry's level, the louder it is. A level 1 sentry is slightly harder to hear than a level 3 Sentry; this fact can be used to counter enemy Sentry guns.
- When out of ammunition, a Sentry gun will continue lock on to enemies and attempt to fire, but will instead make clicking sounds.
- Engineers can reach higher standing on a level 1 Sentry gun than with a Dispenser, making it a better choice on jump and puzzle maps.
- Due to a bug, the rockets from a Sentry gun may sometimes damage teammates if the sentry gun is destroyed as the rockets are in-flight.
- An unused alternate kill icon for the level 1 Sentry gun exists in the game files, seen to the right.
- Per the "Loose Cannon" comic, the Engineer's grandfather, Radigan Conagher, had full design schematics for the sentry as early as 1890.
- If a sentry is redeploying, there is a milisecond between the change from level 1 to level 2 (and level 2 to level 3). This allows just enough time to start the Wrangler at a particular level.
- The Combat Mini-Sentry Gun is not it's own model, but is rather a submodel of a level 1 Sentry with the light from a payload cart taped onto it and a checkered pattern on the side.
- Sentry gun is a turent called sentry gun and u can upgade it