My 223 is a fast twist and I shoot the 69 Sierra Match Kings (SMK)... I've killed groundhogs at over 500 yards with it (502 I think if I remember correctly). When shooting steel it doesn't make much of a splat past 500 yards or so but it'll hit the steel accurately out to 800 (very wind limited).
Given a fast twist (like 6.5 in a .223) and the right bullet (80-90gr VLD's), a .223 or .22-250 can be accurate out as far as 1000yds. Some intrepid souls even shoot AR Service Rifles in 1000yd competition (non-BR). *HOT* loads of N540 and JLK 90gr VLD's down a 20" 1-6.5 twist match barrel will get there easily. At 600 they don't give up much, if any, to the various .308 loads. And that should point out there there *are* better choices available, if you aren't constrained for some reason in terms of rifle or caliber.
Back to hunting, I grew up in western Nebraska, i.e the windy Wyobraska region, and spent an inordinate amount of time in any prairie dog town I could get permission for. Pretty much all of my shooting was w/ a .223 Rem (few thousand rounds) and a little w/ a .220 Swift (couple hundred). Not because the .223 is 'better' than the .220, or the .22-250, but because the bulk of the time, that was all I had.
The 'conventional wisdom' put the .223 as a 200-250yd varmint cartridge, and the .22-250 as a 350-400yd cartridge, and the Swift as a 400-450yd contender. Note that this is w/ light bullets, in the 40-55gr range.
In reality, it really depends, IMHO, on the conditions and the ability of the shooter. I'd say the values above are a good safe bet. I know for a fact that I pegged several prairie dogs at a shade over 400yds w/ 52gr TNT's. The flip side of that story is that it took me more than a few rounds to connect, and it wasn't terribly devastating (no 'red mist'). Out to 300 wasn't too difficult, and 350 was pretty doable. I never really got a chance to 'go for distance' w/ the .220 Swift, as the particular towns I had access to pretty much maxed out at about 450yds. It would easily do that far, and I took a few rockchucks here in Washington state at around 400yds w/ it, so it's good *at least* that far. From what I've heard, the .22-250 is in reality good out to 400+, and the Swift, if loaded hot enough, should be good to maybe 500yds.
I would personally rather use varmint bullets than the heavy (i.e. 80 plus grains) target projectiles on light/thin-skinned critters, but that's my own personal perspective. I'm not convinced that a bullet designed to survive being shoved down an 8, 7, or 6.5 twist barrel is going to do more than just perforate the target on contact. But that's my view. YMMV.
Hello again tyler--with varmint bullets 50-55gn in the 223 i have no trouble relying on it to 500yds--since you are new to this the 223 may be a better venture--easy to load for and get components for, no recoil and you can shoot A LOT before the need to rebarrel. With heavy bullets id take the 223 to 800yds and the 22-250 to 1000.
I tried a 243 ack with 70gn blitz xinks at 1040yds (williamsport back bank) my buddy, my girlfriend and myself scored hits on a groundhog silhouette after getting the rainbow all the way out there--neat vapor trail.
I'm doing some experimenting with the 68/69/70 gr. bullets out of a 26"=barrelled AR in .223 AI. I'm getting a good working load that nets around 3100 f.p.s m.v. I've shot 7X9" 1" thick jugs of water with 70 JLK's at 550 and 675 yds., and terminal ballistics were not explosive at all. The 69 gr. Nosler Comps. were explosive on 600 yd. gallon jugs at a similar velocity. All this is to try and determine the maximum range which the .223 is effective for shooting coyotes. I shot a coyote last year @ 550 yds. with a 69 gr. Nosler, and it was killed quickly with a nickel size exit wound, but nothing at long range since.
I don't feel that I'm intrepid, BUT I do use my AR service rifle in 223 out to 1000 yards. I shoot 90 jlks from 600 to 1000. The ballistics for the wind drift are identical to 308 Win and 190 Sierras from a 26 inch tube.
My ammo is hot but not HOT. IE the pressure has been measured at about 55Kpsi.
As to killing-- the longest kills I can manage with my open sights are on deer around 550 to 600 yards and the 75 amax works well with signs of decent expansion. Personally I'd doubt that further out or with the MK type bullets in this cartridge thought. I've seen many of the 80 smk, 80 JLK, 80 Berger, and 90 jlks laying in the impacts at 600 that look good enough to shoot again. And though a 223 pencil hole will kill, I doubt it would be impressive at all.
Get as close as you can, but utilize your skills as needed.