Assault rifle

The assault rifle is a moderately heavy, burst-firing weapon in RimWorld which fires a burst of three low-damage shots, has a faster firing rate, moderately long range, and good accuracy. With these attributes, the assault rifle is a useful weapon to put in the hands of a decent shooter to put a few well-placed shots in enemies at longer distances, and frequently too. The considerably high accuracy, decent range, and high fire rate make the assault rifle a versatile weapon - but although it's good at a multitude of aspects, it doesn't excel at anything, so there are often better weapons to use for the roles that the assault rifle can assume.

As previously touched on, it's advisable to equip a considerably accurate (97% or more) shooter with the assault rifle to take good advantage of its longer range, although a less accurate (96% or more) shooter will suffice when using it in the region of 20-25 tiles instead of the full 31.

Due to the low damage per shot, the assault rifle doesn't fare very well against armored opponents such as mid-late game mercenary raiders, insectoids, or mechanoids either.

Obtaining

The assault rifle can be purchased from outlander combat suppliers and towns, and also from orbital weapons traders - all at a considerable cost. The assault rifle can also be manufactured at a machining table once the machining research has been completed, for 60 steel, 7 components, and 45,000 ticks (750 secs) of work.

Conclusion & Comparison

As previously mentioned, the assault rifle lacks a compelling reason to really use it other than its versatility. While it's all-round superior to the considerably cheaper machine pistol, the following weapons are generally better choices for the given scenarios:

Pump shotgun for close-range damage output.
LMG for close-medium range damage output
Bolt-action rifle for picking off more-distant targets.

However, the former two weapons may not necessarily be the best class of weapons to compare the assault rifle to; while the assault rifle has both a little bit of DPS and good accuracy/range, it leans more towards the latter class of weapons (along with the bolt-action rifle and sniper rifle) than anything else.