SMT PLT MAKES UNAUTHORIZED CONTACT APCH IN LESS THAN VISUAL CONDITIONS TO A NON TWR ARPT.

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I WAS CLRED FOR THE APCH TO THE OGM (ONTONAGON; MI) ARPT (NDB) AND WAS APPROX 8 MI TO THE SW (COMING FROM IRONWOOD; MI APART) AND CLRED OVER TO CTAF AT 3500 FT MSL. WHEN I ARRIVED OVER THE ARPT/NDB I SAW THE RWY AND DECIDED TO DSND TO LAND IN WHAT I WOULD RATE AS CONTACT APCH TYPE CONDITIONS; PROBABLY 2 MI VISIBILITY AND MAINTAINING CLR OF CLOUDS. THIS WAS ACCOMPLISHED BY CIRCLING OVER THE RWY WHILE DSNDING. THE APCH AND LNDG WAS A NORMAL EVENT FOR A CIRCLING APCH. THE WX AT THE TIME PRIOR TO LET DOWN CONSISTED OF SNOW SQUALLS WITH CLOUD TOPS AROUND 4500 FT MSL AND BROKEN. GND CONTACT CAME AND WENT PRIOR TO ARRIVING AT THE NDB TO DO THE FULL APCH; AND I WAS THINKING I MAY BE ABLE TO DO A CONTACT APCH BUT DID NOT GO BACK TO CTR FREQ TO SEE IF I COULD GET A CONTACT APCH CLRNC. CTR ORIGINALLY CLRED ME FOR A VOR APCH AT THE ARPT BUT I READ BACK 'CLRED FOR THE NDB APCH' AS THERE IS NOT A VOR APCH PROC FOR THIS ARPT. AFTER HEARING THIS IT WAS A LITTLE CONFUSING; I THOUGHT; ON THE CTLR'S PART FOR NOT KNOWING WHAT APCHS WERE AVAILABLE AT THAT ARPT. ANOTHER FACTOR FOR NOT RETURNING TO CTR FREQ AND REQUESTING A CONTACT APCH WAS FROM PREVIOUS TRIPS TO THE AREA KNOWING RADIO RECEPTION WASN'T GOOD AT ALTS OF 3500 FT AND LOWER; AND DECIDING I HAD ADEQUATE CLOUD CLRNC AND VISIBILITY TO PERFORM A CONTACT APCH AND WOULD CANCEL IFR CLRNC OVER TELEPHONE. AFTER REVIEWING AC 61-27C INST FLYING HANDBOOK PAGE 215; I CONCLUDED THAT I SHOULD HAVE DONE THE FULL APCH TO THE ARPT REGARDLESS OF THE BETTER FLT CONDITIONS I ENCOUNTERED HAVING NOT GOT AMENDED CLRNC FROM ATC FOR A CONTACT APCH. I DON'T BELIEVE THERE WAS ANY OTHER AIR TFC IN MY AREA.