.040 this is more to my liking.I have a 16" galil with the gas port 6" from the breach face (16" micro galil) that works like a dream with a .040 gas port.
if I was not going to be cleaning the 17-223 some thing like every 10 shots I would avoid the small hole stuff as it may foul shut but I really am trying to get this thing be as accurate as possable no mattter how much F!@# around i have to do to keep it cycling. I am thinking an acess hole for cleaning the port would be a good idea. Of course now that I have the reamer There will be a 17-223 light weight version and a pistol as well. I have no good reason for building the pistol other than it will be the only one on earth.