VFR BE33 INBOUND AT SLN HAS NMAC WITH ASTRA JET.

Narrative

WE WERE IN THE TFC PATTERN FOR RWY 17 (R TFC) MIDWAY THROUGH OUR DOWNWIND; TWR CALLED TO TELL US TO MAKE A L 360 DEG TURN FOR TFC AND WE WOULD BE #3 BEHIND THE ASTRA ON A 6 MI FINAL. MY STUDENT ACKNOWLEDGED THE CALL. I UNDERSTOOD US TO BE #2 -- I HAD NOT HEARD CORRECTLY. DURING OUR FIRST TURN; I REQUESTED ANOTHER TURN TO GIVE US MORE SPACING FROM THE INCOMING ASTRA. AS WE BEGAN OUR SECOND 360 DEG TURN; I SAW AN ASTRA LAND. I TOLD MY STUDENT THE ASTRA WAS ON THE GND. AS WE FINISHED OUR SECOND TURN; I TOLD MY STUDENT TO BEGIN HIS APCH TO RWY 17 BECAUSE THE ASTRA WAS ON THE GND. WE STARTED OUR BASE. AS WE NEARED FINAL; TWR ORDERED US INTO AN IMMEDIATE TURN N (LEFT) TO FOLLOW OUR ASTRA TFC. AS WE TURNED N; WE CAME HEAD-ON WITH THE ASTRA. WE BOTH DID TURNS TO OUR RESPECTIVE LEFTS AND AVOIDED EACH OTHER. THE BLAME IS IN MY MISUNDERSTANDING OUR SEQUENCE. I DO BELIEVE THAT HAD TWR TOLD US THAT WE WERE NOW #2 AFTER THE FIRST ASTRA LANDED; I MAY HAVE CAUGHT MY MISUNDERSTANDING. THE PROB WAS COMPOUNDED BY 2 ASTRA'S ONE RIGHT AFTER ANOTHER WITH SIMILAR CALL SIGNS. I BELIEVE I HEARD THAT WE WERE #2 INSTEAD OF #3 IS BECAUSE THAT IS WHAT I HAD EXPECTED TO HEAR.