Assuming you have a post '66 rifle, the rear most screw in the trigger piece controls the safety. It should be screwed in until it just touches the safety, when the safety is engaged, either fully (locks the bolt) or in the unlocked position. If this screw does not touch the safety, the trigger piece can release the sear regardless of the safety position. The sear engagement is only about 0.015", so it don't take much movement of the trigger to release the sear.
Pre '66s had the screws in the safety and they adjusted to the trigger piece instead of as above. The action, although opposite, was much the same though a tiny amount of slack in the safety screw allows the sear to be released.
