This might be half of what you want. From the UK MAIL newspaper online service that interviewed the pilots of the UK's first AH-1 attack mission in Rahim Kalay, Afghanistan in the summer of 2007. About half way down they speak of shooting 20 round bursts at their targets though twice they shot short bursts of warning shots, and at one mention a 10 round burst. But again when engaging the enemy it was all 20 round bursts. Otherwise I'll check Global Security to see if they have any USA FMs on the topic.
http://www.dailymail.co.uk/home/mosl...g-Machine.html
Regards,
Pat