I've D&T a couple of the Gustav receivers and one Steyr. Yes, they are both surface hardened. However, I had no real problem drilling thru the surface hardening into the receiver with a drill bit. Used an appropriate drill bit and tap bought from either Graf's or Midway to do this. Had a darn hard sharp pointed awl/punch and was able to ping their receivers so my bit stayed centered when I drilled thru the receivers using my drill press. Tapping the holes was no problem.
Now if you had a U.S. M1917 Eddystone or a 1903 Springfield receiver, I write yep on the surface hardening and be prepared for a problem drilling. And you better have a carbide drill bit handy to use. If you can drill them, then be prepared having a problem running the tap into the drilled hole. In short, darn hard metal in their receivers.. Matter of fact, a couple of local elderly gunsmiths that'd worked on many a Springfield or Eddystone receiver in the past, basically didn't want to drill and tap these receivers for me......too much a hassle due to their hardening treatment.
Last edited by huffmanite; 06/18/17.
