they are a stacked tube blowback. solid markers, they have 2 minor flaws that are easily taken care of.
1) DO NOT DRY FIRE A RAPTOR. The valve is brass, and will quickly mushroom into an unusable mess.
2) they have been known to chop unless a minor mod is done. If you are rapid firing your Raptor and haven't installed the anti-double feed mod, expect ro chop once or twice a hopper. The mod costs a few cents.
They are a solid performer, but there are no easily obtained upgrades except barrels.