Not entirely firearm related... but there was a U.S. Olympic Archer in the last summer games that listened to speed metal at a high volume while practicing... not sure if they allowed ti while competing, but I would imagine they did because I can't see the guy practicing in a manner that he couldn't repeat for competition.
Anyhow, my point is that it seems counter productive, but this guy was one of the finest in his field and he was pounding the music while plying his trade.