I have noticed on the butt plate of the BAR rifle there some type of a "flip up" attachment at the top where the rifle would be placed against the shoulder when firing. What is this for? I noticed it on the weapon supplied with one of my Dragon figures. These 12" figures have excellent detail by the way.

its called a hinged butt-plate..
http://www.ww2gyrene.org/weapons_BAR.htm
http://www.rt66.com/~korteng/SmallArms/barnom.htm
a similar thing is fitted to the British Army L86 light support weapon..
[url]http://www.defence.co.kr/html/bbs/data/smallarms1/1-1-1-1L85-86.jpg[url]
it just gives a bit of support and some extra stability and control when firing.

ps ..just noted the www.defence.co.kr link to the jpeg is u/s..sorry

http://www.defence.co.kr/bbs/bbs.cgi?db=smallarms1&mode=read&num=3893&page=4&ftype=6&fval=&backdepth=1
http://world.guns.ru/machine/mg37-e.htm
..a couple of L86 pics..

It also means that you have both hands free to change magazines etc. without dropping the gun from the shoulder. IIRC Brens had them too.