Experimental weapons are futuristic weapons that don't fire casual bullets. Instead they fire special rays or grenades which in most cases have chance to affect enemies with status effects while their custom variations do that automatically. Most of Experimentals have medium range similar to Machine Guns, but Rail Gun is highly accurate long range weapon similar to a Sniper rifle, while DSR1 fires white bouncy grenades. Unless you use the Rail gun, Experimentals aren't recommended for Sniper class as snipers are bad on closer range due to their low health.
Experimentals are actually made of advanced weapons that are actually weapons of other types.
Rifles - The Pulse Rifle.
Shotguns - Ion Cannon is a shotgun as it fires multi shot and has similar fire rate and close range like any shotgun.
Machine Guns - Laser Cutter has extremely high fire rate, lots of ammo, but bad accuracy and close range (closer than most of machine guns).
Snipers - Rail Gun is an advanced sniper. It has the longest range, high damage and extreme accuracy.
Explosives - DSR1 is a grenade launcher, but grenades it fires don't explode. But like with Explosives, you can harm your squadmates and yourself with it.
Elementals - All Experimentals except DSR1 have chance to affect enemies with elements, and there is one weapon for all 4 elements, except DSR1 which fires unknown white balls, just like Bad News is the only Elemental without element, that fires a white ray.