The "Sapling" was the standard rifle chassis for most of the history of the Empire of 1,000,000 Suns. 

History

First developed during the 1,000 Years war, it saw continuous service (albeit with many variations and upgrades) until the period between the Great Reckoning and the War of the Empires.  Many later claimed that the E1MS might have won the War of the Empires if they had stuck with their traditional arms instead of upgrading to higher tech designs provided by the remnants of the Planetary League.

The E1MS also used the Sapling as a foreign policy tool, gifting it (or the designs to build it) to nearly anyone willing to fight the enemies of the Empire. 

The Cult of Troniac also made extensive use of the Sapling, (especially during the 1000 Years War), as many early conversions to the faith were robots that built the Sapling in the Empire's military machine.

Over time, this weapon was produced in such large numbers, and the designs to create it were so widely available, that most criminal enterprises, insurgencies, and warring factions throughout the galaxy had at least a few of them in their armories.

Variants

There were three main variants of the Sapling in use throughout most of its career. 

The first was the laser rifle, which was the most widely used as it required only electricity to operate, and was therefore the simplest to keep in service.  It was also the cheapest to mass-produce.  This simplicity was offset by the fact that a foe could deflect the laser by presenting an appropriately reflective surface.  Most laser rifles could be switched between "single shot" mode, which activated the laser briefly, and "continuous beam" mode which would operate until either the trigger was released or the power cell discharged.

The second main variant was the rail-gun, which used electromagnets to launch kinetic projectiles.  This necessitated carrying ammunition in addition to power cells.  The projectiles came in a variety of variants with various properties, such as armor-piercing, hollow-point, etc.

The third, and most complex of the standard variants was the plasma-bolt rifle.  This version launched a magnetic core surrounded by charged plasma.  It had the most complex ammunition, consisting of a power cell, a magazine of cores, and a cylinder of gas.  This was a logistical hassle that helped make this the least used of the main variants of the Sapling.  In addition to the damage caused by the magnetic core (its self a kinetic projectile), the plasma fired by this weapon could damage electrical circuits, super-heat armor, and burn flesh.  If the specialized ammunition was unavailable, this version could also fire the projectiles made for the rail-gun variant as well. 

Accessories

Being such a widely-produced weapon for such a long time lead to a plethora of accessories and modifications being created for the Sapling from the mundane to the exotic.

Other Notes

The Sapling rifle was designed to be used by Cielioids, and as such, the trigger is about twice the size as what a human would normally use.  (Cielioids have only two large fingers on a hand about the same width of a human hand.)  This makes operation of the rifle by humans awkward, but not by any means impossible.  During Era-2, one of the most popular modifications for the Sapling was to replace the handle and trigger with something more amenable to human hands.