A BE02 FLC EXPERIENCED AN NMAC WITH A PA31 WHILE FLYING A PUBLISHED SID IN MVFR CONDITIONS. THE CAPT CLAIMED THAT IF THE FLC HAD NOT BEEN RUSHED DURING TKOF; THEY WOULD HAVE BEEN MORE FAMILIAR WITH THE SID WHICH WOULD HAVE FREED THEM TO SCAN OUTSIDE THE ACFT FOR TFC.

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NAS PT MUGU RADAR WAS OTS; RAGGED CLOUD DECK; VARIABLE 2800-3500 FT AND LIGHT RAIN SHOWERS THROUGHOUT THE AREA. WE WERE DEPARTING OXR ON A SKIFF4 DEP AND ANOTHER COMMUTER FLT WAS BEING VECTORED IN ONTO THE LOC RWY 25. UPON REACHING THE RWY; TWR REQUESTED AN IMMEDIATE TKOF FOR DEP CTL PURPOSES. AS A RESULT THE FO AND I ONLY HAD TIME TO GLANCE AT THE SKIFF4 DEP SID; WITH VTU TRANSITION. THIS CAUSED CONFUSION IN THE AIR RESULTING IN A LATE TURN WBOUND TOWARD SKIFF. UPON SWITCHING OVER TO PT MUGU DEP; THE CTLR ORDERED US TO STOP AT 3000 FT VERSUS THE INITIAL 4000 FT CLRNC; AND TO RPT SKIFF. UPON REACHING SKIFF WE RPTED OUR LOCATION AND BEGAN TURNING TOWARD ROBOR AS REQUESTED BY PT MUGU DEP. THE FO IMMEDIATELY SPOTTED A LIGHT TWIN (POSSIBLY A NAVAJO CARGO FLT) FLYING UNDERNEATH US R TO L 200-300 FT BELOW US; AND LESS THAN 500 FT AHEAD OF US. WE CONTINUED EBOUND; INBOUND ON THE 089 DEG COURSE TO VTU AND THE OTHER ACFT OPENED THE DISTANCE AS IT TRAVELED TOWARD THE NE. WITHIN 30 SECONDS AFTER THE NMAC WE ENTERED IMC CONDITIONS. WE CALLED PT MUGU APCH AND QUERIED HIM IF HE WAS TALKING TO ANYONE ELSE. HE RPTED HE WAS ONLY TALKING TO US AND THE OTHER COMMUTER FLT. WE CALLED THE OXR TWR LATER AND THEY RPTED THEY WERE NOT TALKING TO ANY OTHER ACFT EXCEPT FOR A FLT OF HELIS (BELL JET RANGERS) DEPARTING AFTER US; AT LOW LEVEL. OBVIOUS CASE OF AN ACFT ATTEMPTING TO TRANSITION AIRSPACE UNDER VFR IN MARGINAL VFR CONDITIONS THAT WERE TURNING INTO IMC. MY MISTAKE WAS IN ALLOWING THE FLT TO BE HURRIED AT TKOF; PRIOR TO ENSURING THAT THE FO AND I UNDERSTOOD THE SID. OTHERWISE WE WOULD HAVE BEEN AT A DIFFERENT LOCATION AT THAT TIME; AND AT LEAST ONE OF US WOULD HAVE BEEN SCANNING OUTSIDE THE COCKPIT.