One of the "innovations" in 30k is the Volkite Weapon range. In short, these are ray guns that are capable of devastating flesh and organic matter with ease.
The background fluff for the Volkite weapon range notes that these nasty Martian inventions were originally intended as mass produced weapons for the space marine Legions. Due to the pressures of the ever expanding Crusade, the humble bolt gun eventually surpassed the Volkite range due to flexibility (i.e. different rounds were easy to load) and were easier to produce.
But are they any good?
Like Bolt weapons, there are a number of options. The Volkite Serpenta is the pistol equivalent, the Charger is the bolt gun analogue and the Caliver is the heavy bolter switch -- roughly speaking at any rate.
There are two major differences. The first is the range. For the Volkite weapons, they're much shorter ranges. For the pistol - its a mere 2 inches shorter, and frankly that's not much considering that bolt pistols are usually only fired on the way in to close combat. For the chargers, they are only 15 inches versus the 24 inch range of the bolt gun. That said, they are assault 2. Bolters will only get two shots if they rapid fire, and that's a 12 inch range. So they're looking rather okay here! Meanwhile for the Caliver, they're heavy 2, at a 30 inch range. This is strictly worse than the heavy bolter in both range and sheer number of shots.
The second main difference is the strength. This is where the Volkites make up for their shorter ranges. They're typically one extra pip in strength than the bolter family of weapons. This means that they're actually more effective
What really sets them apart is the deflagrate rule though. This rule causes additional automatic hits according to the number of wounds the initial volley caused. This, plus the combined strength, is what makes them deadly at taking out plenty of enemy infantry.
I regard them as worth taking, but wish that more squads in 30k had access to them!