If I were going to go with the .223AI in an 8 twist, are there any decent factory guns available or do I need to go custom?
Just have one built. Go with a Rem700 action to keep things simple, you'll have like 18 zillion aftermarket options on stocks, triggers, etc, and be sure to give the smith a dummy round loaded mag length with a 75 Amax and tell him you want to be able to reach the lands.
However..... having built a 8 twist .223AI with my own two hands, it doesn't really light my candle. I don't need THAT low of recoil, and while it's fun, it's limited compared to a real LR cartridge. It's a good trainer for my kid but I find I don't shoot it much. YMMV.
Personally, my opinion is if you want a low-drama, turnkey, (relatively) low recoil long range toy, just get a Creedmore. Easy brass availability, great bullets and lots of them, will be twisted right, etc.
If you want to step it up from there and get about the most LR bang for the recoil, the cool kids are building 6.5 SAUMs (aka 6.5 GAP 4S). GAP is selling headstamped Hornady brass. You can run it on the cool side, still beat 6.5/.284 ballistics, yet triple the barrel life of the 6.5/.284, which other than THAT little detail, would be another good choice.
Google 6.5 GAP 4S and settle in for a looooong night of reading. Some good people have got a good recipe going there.
I'm building a midweight one now... should be done this winter. Won't get the barrel and stock till early 2017.
When comparing the various cartridges, compare drift numbers. Therein lies your huckleberry. Minimize recoil, minimize drift, ignore all the typical gun-store ballistics gack you might've heard ("it shoots so flat I can hold on hair out to blah blah blah...").... Drift. Did I mention to compare drift?
