The M16A1 assault rifle. Happens to have some "shock" ammo that can be selected with the "C" key. Although extremely weak (only very tiny holes if any), said ammo makes very loud crackling on impact which may be useful when you're being Hunted (wink nudge). Too bad there aren't any NPCs like spiders that could be stunned. Besides that, it's just... an ordinary M16A1.
Featuring projectile impulse, spread system, and gun recoil. Try not to spray and pray, use controlled bursts and let the weapon settle down between bursts.
Now features support for Dima's destructible robot framework.
Credits to Cresta for the projectile handling code.
PS I recommend the Subnautica Alien Rifle or other railgun mods with this gun, though it's not a requirement.