FALLON, Nev., May 29. (IP)-- The murder case against Joseph C. Silvey, 55-year-old former Sparks railroad boilermaker, ended speedily in district court today as he pleaded guilty to second degree murder and was sentenced from 10 to 20 years in the state prison. - entered plea before District Judge Clark Guild - accused of fatal shooting on March 19 of Mrs. Mahnen, following a quarrel - unsuccessful attempt of suicide - guilty plea after charges reduced from first to second degree murder