Got this from Fulton Armory site:
On Fed Ord Receivers...
by Clint McKee
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Clint, tell us about Fed Ord receivers
Many (most) of the Fed Ord M14's are unsafe to fire, IMHO. The company is no longer in business, so you have no warranty recourse.
They came in 2 flavors: Fed Ord receiver made for G.I. bolt & all G.I. parts (best case scenario since if the receiver is no good, at least you have some good parts); Fed Ord receiver made for Chinese bolt & all Chinese parts (worst case scenario, bad receiver & bad parts).
The common problems with the receivers include poor/no locking lug contact on one or both locking lugs of receiver/bolt interface; very poor op rod rail on receiver, causing op rod to fall away from bolt roller; rear sight receiver elevation serrations very shallow/non existent;
Hope this helps.
Clint McKee