(1) The layout of this ammo dump is the same as the last one, only different powerups are scattered about. Most crates here contain only clips, so ignore any crates not mentioned unless (for some reason) you are in desperate need of 9mm ammo. Ready? Open the door, spin right, and blow the secret wall. Run ahead to the pulse rifle magazine (grabbing and activating the shoulder lamp on the way makes it a bit easier to see but is not necessary). The auto-map you pass will also make navigation easier.
(2) If you need them both, continue forward for the shotgun shell (behind the secret wall straight ahead) and acid vest (behind 2 secret walls on the left). If you only need shotshells, however, you should leave this one be and try to make it to the trio of shells right at the end of this level.
(3) Backtrack past the entrance and blow the crate at the top left of the stairs for seismic charges and pulse rifle grenades. Remember: use your charges for walls; save the grenades for more animate targets until you run out of seismics! Blow the left wall at the top of the stairs and then 5 more walls to arrive near the exit door. Grab the pulse rifle, flame thrower, and any med kits you may need on the way. You can grab the shoulder lamp if you want, but you don't really need it since that first one will last to the end of this level.
(4) In the exit room, grab the shotgun shell (in the crate ahead and on your left as you enter) and 2 seismic charges before heading up the unexplored stairs.
(5) Now blow the secret wall opposite that previously-blown wall at the top of the stairs and grab the 2 med kits and 3 shotgun shells (if you went after the acid vest and shotgun shell earlier, you won't make it this far). If you manage to grab this much stuff, you're doing well.