When you go to the Water Caverns, go to the Com area where the radio is to contact Jack Wade. As soon as you enter the room kill all the guys in the room. Go to the right hand corner where there are strips of glass in the wall. blow all the crates in that corner and in one you should see a smaller box come out. Blow all the boxexs in that crate and you should see two computers come out. Blow them and you will find two AR33s. Pick them up and you will have double Assault Rifles.