You're forgetting that Dredgen Yor wasn't a Guardian anymore. He was wielding the power of the Darkness. That could have made him withstand the first shot. Also, how do we know he didn't die from the first shot? It seems like Yor was manipulating Shin, in a "join the Dark side" kind of move. Shin was perhaps provoked to fire out of rage and then most likely shot Yor more times than necessary.