whats up BAR ?

Purchased a BAR longtrac in 7 mm rem. Bought VX3 scope. Cant get it to group at all. Is tbeir any problems out their with this gun? Yes the mounts are tight and torqued,tried winchester, Hornady, and Remington. Nothing will group better than 6 to 8 ". Thats in a vice, sandbags, anyway you want to shoot. At 100 yrds the group is a little better not much. 200 yrds is where I need the zero for this rifle. Tried scope on another rifle no problems which was also a 7 mm. I'm beginning to believe the aluminum reciever is not stable. Any ideas, suggestions are more than welcome beautiful rifle, may soon trade in and grab a Sako, I've just always wanted a BAR thinking different now. Thanks