Mini-turret

Improvised Turret Gun

The improvised turret is a stationary defense mechanism which automatically fires at any enemies (psychotic animals / raiders) entering its range of 25.9 tile radius. It fires a 3-round burst with no need for warmup, has a slow 5.15 second cooldown and 96% per-tile accuracy. While turrets are somewhat underwhelming on their own, large groups of turrets are able to incapacitate or kill small groups of hostiles within seconds.

It has a target size of 68% making them harder to hit.

Turrets have a 50% chance of exploding when it reaches 20% health.

Construction

Constructing the turret requires research in microelectronics basics and gun turrets (some scenarios have Gun Turrets already researched).

Alternatively, it can be opportunistically uninstalled and looted from various world sites.

Material	Steel Cost	Cost	Hit Points	Flammability (%)	Market Value	Beauty
Steel	175	3	100	20	405	-60
Plasteel	100	3 + 75	280	10	1,320	-60
Uranium	100	3 + 750	250	0	4,765	-60
Silver	100	3 + 750	70	20	1,010	-60
Gold	100	3 + 750	60	20	7,760	-60

Notes

Steel is the most viable option early-game, but it's advisable to switch them out for plasteel turrets as soon as you can, as steel turrets aren't very durable and therefore can't withstand sustained gunfire.
The most effective material is plasteel. It has the most HP, very low flammability, is somewhat easier to obtain mid-late game, and saves steel for other purposes.
You should expect turrets to be frequently replaced, and uranium is too rare and expensive to be practical.
Regardless of what material is used, turrets have -60 beauty.
Silver and gold are poor material choices; they may actually increase the strength of raids (due to increased colony wealth) and aren't very durable.

Images

Steel Improvised Turret
Plasteel Improvised Turret
Uranium Improvised Turret
Steel Improvised Turret
Golden Improvised Turret

Tactics

Used alone or in small numbers, turrets do not provide much additional firepower. However, raiders will often target the turret instead of the colonists if it is closer to them, shielding the colonists from harm until the turret is destroyed. However, attackers will not take an unpowered turret as a primary target. The firepower of the turrets adds up when massed together, to the point where turrets alone can sometimes beat back even massive raids. Larger colonies often build a "killbox": An entrance area designed to funnel raiders where turrets can do maximum damage while the raiders' own ability to fight back is minimized. Using Sandbags to protect your turrets can be a solid tactic in either case.

When building a turret, there's a 50% chance that it will never explode; regardless of what amount of health it's at. Normally; a turret will spark and emit a hissing sound that increases in pitch, once it drops to or below 20% of its maximum HP (e.g. a Steel Improvised Turret will begin hissing at 20/100 Hit Points), and explode a few seconds later. When a turret's about to explode, all nearby raiders will run in an attempt to get out of the blast radius to keep their skin intact.

When a Turret explodes; it does 200 damage to all structures within its radius, 50 damage to the slag chunks and components that drop, and typically 12-48 damage (with variances in increments of 4 points) to all pawns unlucky enough to get caught in the explosion.

Example of an Explosion

Trogo is attacking a Steel Turret with his Awful Wooden Shiv. It's at 21 HP, but it's still fine.

The turret's now at 20 HP and begins to spark and hiss - Trogo's in danger.

The turret has now exploded: Trogo's wounded, structures are damaged - all hell's let loose. Took several screenshots and merged them into one image to demonstrate the full extent of the damage.