PILOT OF SMA REPORTS NMAC WITH LIGHT TWIN IN TRAFFIC PATTERN AT SOP. REPORTER IS USING WRONG CTAF FREQUENCY.

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AFTER CANCELING MY IFR CLRNC AND QUICKLY DSNDING ON A SLAM DUNK DSCNT TO MOORE COUNTY ARPT; MY COPLT ANNOUNCED ON 122.7 OUR INTENTION TO ENTER A L-HAND PATTERN ON A L XWIND LEG FOR FULL STOP LNDG ON RWY 23; WHICH I DID. THERE WAS A 3 KT WIND FAVORING RWY 23. SHORTLY AFTER TURNING L DOWNWIND; MY COPLT LET OUT AN EXPLETIVE AND GRABBED THE YOKE TO TAKE EVASIVE ACTION TO TURN THE AIRPLANE TO THE R. I IMMEDIATELY LOOKED UP AND SAW A PISTON TWIN ENG AIRPLANE JUST TO THE L OF US VERY CLOSE TO OUR ALT; AND I ALSO ASSISTED IN THE EVASIVE ACTION TO TURN OUR AIRPLANE TO THE R. THE TWIN WAS IN A SLIGHT L BANK. WE BARELY MISSED HITTING THAT AIRPLANE HEAD-ON. AFTER LNDG; WE DISCOVERED THAT THE OTHER PLANE HAD LANDED ON RWY 5; APPARENTLY FROM A R-HAND PATTERN. THAT AIRPLANE QUICKLY DEPARTED BEFORE WE HAD A CHANCE TO TALK TO THE PLT. WE ASKED THE ARPT LINEMAN IF 122.7 WAS THE CORRECT CTAF; AND HE INDICATED IT IS 123.05. I THEN ASSUMED THAT THE APCH PLATE FROM WHICH I GOT THE FREQ WAS NOT CURRENT DUE TO AN ERROR IN POSTING TERMINAL PLATE REVISIONS. LATER INVESTIGATION YIELDED THE FACT THAT I WAS MOST LIKELY LOOKING AT THE APCH PLATE FOR THE WRONG ARPT; THAT OF MONROE COUNTY; NC; INSTEAD OF MOORE COUNTY; NC. THE FACTS THAT THE ARPT NAMES ARE VERY CLOSE IN THE ALPHABET; SOUND; AND APPEARANCE; THEY BOTH HAVE A SINGLE RWY ORIENTED 5/23; THEY BOTH HAVE A GPS 23 APCH; AND THE RWYS ARE NEARLY THE SAME IN LENGTH MADE THE ERROR LESS APPARENT. MY COPLT QUESTIONED WHETHER OR NOT THE ARPT NAME WAS CORRECT; FOR THE APCH CTLR HAD REFERRED TO THE ARPT AS SOUTHERN PINES. WHEN I LOOKED UP THE ARPT IN MY FLT GUIDE DURING PREFLT PLANNING; I REMEMBERED THAT THE ARPT HAD 2 NAMES; SOUTHERN PINES/MOORE COUNTY (REMEMBERED INCORRECTLY AS MONROE COUNTY); SO I FELT ASSURED THE ARPT NAME ON THE PLATE WAS CORRECT. AS A RESULT; WE HAD XMITTED OUR ANNOUNCEMENT TO ENTER THE PATTERN ON THE WRONG FREQ; AND HENCE THE OTHER PLANE DID NOT HEAR US; AND WE DID NOT HEAR WHATEVER XMISSIONS THEY MADE EITHER. ON OUR NEXT FLT LEG; WE LOOKED IN THE GNS530 DATABASE ON BOARD AND FOUND THE CORRECT FREQ TO BE 123.05. AFTER TALKING MORE TO MY COPLT LATER; HE INDICATED TO ME HE SAW THE OTHER PLANE ENTER THE PATTERN FROM A 45 DEG TO THE R DOWNWIND FOR RWY 5 AND IT TURNED TO THE L RIGHT TO INTERCEPT THE R DOWNWIND DIRECTLY IN FRONT OF US. NEITHER MYSELF NOR MY COPLT REMEMBER SEEING A SEGMENTED CIRCLE. PUBLISHED DATA ONLINE AND IN AIR GUIDE PUBS 'FLT GUIDE' INDICATE L-HAND PATTERNS AT SOP.