FLT CREW OF H25A TURN WRONG DIRECTION AFTER DEP RWY 4R AT MDW.

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I WAS THE FO ASSIGNED TO THE TRIP; OCCUPYING THE L SEAT AND ACTING AS THE PF. DURING TAXI OUT TO RWY 4R AT MDW; THE CAPT (PNF); BRIEFED THE MIDWAY 4 DEP SINCE THERE WAS ONLY ONE SET OF CHARTS ON THE AIRPLANE. HE STATED THE DEP AS 'TURN R CLB ON HDG 100 DEGS UNTIL LEAVING 240OO FT THEN WHATEVER IS ASSIGNED.' SINCE HE WAS READING OFF THE CHART; I ACCEPTED THE INSTRUCTIONS. TWR CLRED US FOR TKOF AND SAID; 'AFTER DEP; TURN L HDG 250 DEGS.' A NORMAL TKOF WAS ACCOMPLISHED. ONCE AIRBORNE; I STATED 'TURNING L TO 250 DEGS.' THE CAPT IMMEDIATELY STATED; 'DO NOT TURN. THE DEP STATES TO TURN R TO 100 DEGS INITIALLY.' I STATED AGAIN; THAT IS NOT CORRECT; TURNING TO 250 DEGS. AS I STARTED THE TURN; THE CAPT RAISED HIS VOICE AND SAID; 'TURN R; R TURN TO 100 DEGS.' I DID NOT WANT TO ARGUE AND TURNED R TO 100 DEGS. AFTER A FEW MI; DEP TOLD US THAT WE WERE TO MAKE A L TURN TO 250 DEGS. THE CAPT THEN SAID HE HAD MISREAD THE DEP INSTRUCTIONS. I BELIEVE THAT IF I HAD BRIEFED THE DEP AND READ IT THOROUGHLY INSTEAD OF RELYING ON THE CAPT; WE WOULD HAVE COMPILED WITH THE DEP CORRECTLY. I ALSO THINK THAT IF I WOULD HAVE HAD THE DEP CHART IN FRONT OF ME; I WOULD HAVE BEEN ABLE TO CONFIRM THE INITIAL DEP INSTRUCTIONS AFTER TKOF.