THAT SNRS ACCELERATE PARTICLES TO CR ENERGIES IS NO LONGER IN DOUBT BUT THERE ARE MANY QUESTIONS YET TO BE ANSWERED. WE STILL LACK DETAILED KNOWLEDGE ABOUT THE EFFICIENCY OF THE PROCESS OF PARTICLE ACCELERATION AT SNR SHOCKS THE EFFECT OF CR PRODUCTION ON THE EVOLUTION OF SNRS AND THE PROPERTIES OF MAGNETIC FIELDS IN THESE SYSTEMS AND HOW THESE ARE AMPLIFIED. IN ORDER TO ADDRESS THESE OUTSTANDING ISSUES WE PROPOSE TO OBSERVE THE SW REGION OF SNR RCW 86 WITH NUSTAR WITH A 200 KS POINTING. THIS WILL ALLOW US TO: (1) DETERMINE THE MORPHOLOGY OF THE NON-THERMAL X-RAY EMISSION IN THIS REGION IN THE NUSTAR BAND AND CONTRAST IT TO OBSERVATIONS WITH XMM-NEWTON AND CHANDRA; (2) CONSTRAIN THE SPECTRAL SHAPE OF THE ELECTRON POPULATION THAT UNDERLIES THE NON-THERMAL EMISSION.