BRIDGEPORT, W.Va. — Black Friday isn’t just when shoppers rush to stores for holiday sales. It’s also one of the busiest days of the year for gun purchases. In the U.S., there are 40 new requests every minute for criminal background checks on people wanting weapons. On Black Friday, the rush accelerates to nearly two checks a second, testing the limits of the National Instant Criminal Background Check System. “We have a perfect storm coming,” said Kimberly Del Greco, a manager in the …