I have a theory as to why pipebombs dont reliably stun scrakes all the time. Have you ever used the m32 on scrakes? If you have you might have noticed that if you shoot it around the knee or below, it knocks the scrake off the ground. Sometimes I see a stunned scrake snap right out of it when a demo tries to blow it up, Im guessing if a stunned scrake gets knocked off the ground, it breaks stun. Now a pipebomb might deal enough damage to stun a scrake, but when its too close or right on the pipe, it gets knocked off its feet and instantly breaks stun. Just my guess.