Indian equity benchmarks BSE Sensex and NSE Nifty50 are likely to make a gap-down start on Wednesday, in a sharp U-turn after the 50-scrip index returned above 18,000 after five months, as a worse-than-expected US inflation reading sent shockwaves across global markets. Singapore Exchange (SGX) Nifty futures — an early indicator of the Nifty index — tumbled as much as 372.5 points or 2.1 percent to 17,719.5 ahead of the opening bell on Dalal Street.