Making Swep bullets go through NPCs?

As I recall, Worshipper’s Mad Cow weapons on GM12 were able to shoot through a few NPCs before the bullet stopped. Can anyone tell me how to recreate this effect for a swep?

This is probably the least helpful solution, but a nocollide, but done in such a way that it passes through and applies damage based on what’s around it?
(constraint.NoCollide)

Not to state the obvious but wouldn’t browsing through MadCows weapon base would answer your question?