Livinus may be on the right track as the action comes most probably from a shotgun. If you could supply a pic of the interior of the receiver (like the one I posted), we could be more ascertive. Another thing you can check inside the receiver is whether the bottom has been hollowed out or not. Then we would know if your action was meant to be shotgun or rifle. I tend to suspect the former origin as, indeed, FN never supplied its actions alone. If built on a shotgun, it won't be as strong as an original rifle but you still have a good rifle, considering that you won't be shooting it that intensively. Also, let's remember that J. Browning's B25 has long been -and arguably still is- one of the strongest O/U actions ever devised. So, maybe the extra-strength built in FN's O/U rifles is more an insurance than a necessity.