I do have 17-223 in ar and works great, excellent accuracy in 18" barrel. for a walk around rifle I would stay away from that heavy KAK barrel shown here. I have not had any of the problems KAK describes in there ad about the 17-223 round. You can order a custom lightweight barrel from BHW to keep things light for a walk around rifle. I have older custom dies made by RCBS I bought used, but really dont use the sizing die, just the seater die. I use a set of RCBS gold medal 223 dies for fl sizing cases, the sizing die uses bushings, so on used brass first use bushing for 22 cal., then again for 20 cal., and and finely for 17 cal., you only need to do that extra work once. All that works better then just running 223 brass in the older RCBS fl 17-223 die. It would be best to have a 20-223 form die along with the older sizing Die. Other options that I did not try are redding makes a 17-223 die set and you can get it at midway, also Hornady makes a 17-223 die set, I myself dont care for Hornady dies. Once your all set up its cheap shooting. 17 cal bullets are very explosive on impact, you really dont need to get max velocity, and to go with that saying, you can have high pressure spikes with small amounts powder variances, if your a sloppy reloader the 17 cal is not for you. For the comment above about 17 fireball, I do like that caliber better for bolt guns, but the brass is very expensive so the 17-223 makes more sense dollar wise. Getting back to the ar platform, on mine I run all lightweight parts for a carry rifle, and it runs flawlessly. KAK is the only one I remember using the term 17-556, all other sources for dies, barrels, ect. use the term 17-223 . Theres been other barrel makers over the years that made 17-223 AR barrels, You may get lucky and find a used one on the classifieds. This caliber was quit popular in the 70's-80's so there are limited supply's out there on the used market.
