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High-speed video (143 kframes/s) and optical spectroscopy (1-ms integration, 188-1100 nm) recorded light-emission events occurring at a railgun by aiming directly down the bore or at the backside of the breech. Blowback was marked by a wave of high-intensity light, smoke, a flame front, and glowing particles traveling back up the bore from the muzzle and lasting up to or beyond 60 ms after launch. Spectra taken down bore and during blowback had signature peaks for alkali metals, AlO, and CuO. Estimated radiation temperatures TER were determined by fitting a Planck distribution to the spectral backgrounds. In the bore, TER was between 3700 K and 3000 K at the start of travel and cooler (2500 K) at the muzzle blast. During blowback, TER ranged from 2400 K to almost 4000 K, the combustion temperature of Al particles. Some shots showed TER consistently around 3600 K during the entire blowback period.