(cross-posting from GNA)
Biggun, all I can give you on this is the size for .223 builds (based on my Saiga and Galil barrels) -
5.56x45 Saiga 90 degree .067" # 51 bit 11.9063" (11 29/32") / 302.420mm
That's the smallest from the "factory" stuff. Since I have only a good idea what a 17-223 is, I wonder if there are any AR builds in a similar caliber? 17 hornet or HMR or whatever it is called? What would that use? I wonder if Varmint Al has anything on his web page.
.177 - .067 = .011 so you would still have "enough" barrel around the hole, IMO.