BAR accuracy

has anybody experienced accuracy problems with BARs'(circa 1980-made in belgium/assembled portugal)?

After rechecking stock tightness, and scope/ring/base mounting, i've come to the conclusion that the forearm is causing me problems. Is there a "rule of thumb" for tightness of the swivel stud assembly securing the forearm to the rifle??

There is no consistancy, as to where the rifle will shoot.

All thoughts appreciated.