Pipe bombs is 5.
Try typing dnstuff, to check if you actually get the pipebomb, or if it was a mistake... Else you still can mess up with the controls again.
rite being a nob here, thought i picked up pipe bombs but i didnt they were rockets just havent got the rocket launcher yet so cant use, so pushing 5 does nothin lol, pipe bombs is 6 by the way
As a further note regarding this, when you are using the full hud in the game, you should be able to see the weapons bar in the lower middle, the brightly highlighed weapons are the ones you have... :)