It may also be this: http://en.wikipedia.org/wiki/Barrett_XM500
http://ariefindra.files.wordpress.com/2009/05/xm500.jpg
mainly because this is a weapon in development NOW, so by the time of the setting of the game, it may be in use. It is also in the bullpup configuration like the M95 but it seems like the XM500 would be more appropriate for the setting of arma 3
Note: image in discussion is from the arma3 official youtube channel http://www.youtube.com/arma3official