around the thickened pole region thus the thickened pole region acts like a slide plane or slide surface allowing jet material to flow around it for this reason the thickened pole area is tapered into a conical geometric form at its extremities the portion of the jet formed by 34 sliding 34 over the thickened pole proceeds at a faster velocity than for a uniform wall thickness liner but particulates breaks up into particles early this produces the high speed precursor jet later the thickened pole region begins to move forward and is joined by the remainder of the collapsing liner material then the remainder of the formation process proceeds as that of a hemispherical liner and the main jet is formed resulting in larger diameter particles traveling slower than any of the particles of the precursor jet the spacing between the two jets can be regulated by altering the material wall thickness or by tapering the wall of the main hemispherical liner the spacing between the two jets can also be controlled by varying the height and diameter of the thickened pole region an optimum diameter of the thickened pole region is believed to be 20 to 40 percent of the main liner diameter the optimum height of the thickened pole region is believed to be 5 to 15 percent of the liner diameter it is.