I remember something about US made FAL rec. being only locally treated in certain areas, as opposed to the whole thing being brought to temp, quenched, then drawn. I would think warpage would be a major problem with the later. You may be able to get some info. from DS Arms, or Entreprise Arms. It'l depend on who you can get on the phone and weather they feel like sharing info. with you, or not. These rec. are not as hard as many think they are. I've cut DS rec. for L1A1 folding cocking handles, and they cut ok with high speed cutters, as I recall. Try that on an M14 rec. Those things are HARD!
Pete