A competing rifle outperformed the Army’s favored M4A1 carbine in key firings during a competition last year before the service abruptly called off the tests and stuck with its gun, according to a new confidential report. The report also says the Army changed the ammunition midstream to a round “tailored” for the M4A1 rifle. It quoted competing companies as saying the switch was unfair because they did not have enough time to fire the new ammo and redesign their rifles before the tests began. Exactly how the eight challengers — and the M4 — performed in a shootout to replace the M4, a soldier’s most important personal defense, has been shrouded in secrecy. (03:01)