Lucinda Area resident Morgie jones has plead guilty to one of the three federal firearms charges against him.    Jones made that change of plea in an apperance before U-S District Court Judge Donetta Ambrose, in Pittsburgh.    The sole count, to which Jones made this plea, involved his now admitted illegal sales of firearms.    Jones is now scheduled to be setenced, on this lone charge, on October Fifth.    Typically, someone facing this situation might be sentenced to a term of from 18 to 24 months in prison.    Originally, Jones was scheduled to go on trial on June 24th.    It was about one year ago that Jones was arrested, by federal authorities, as part of a probe into alledged illegal weapons sales involving militias.