http://njhighpower.com/cart_tech.htm
Some info on various chambers.
No autoloader has a true .223 chamber. In fact, I don't think any bolt actions do any longer. Manufacturers will NEVER produce something that can explode using any factory ammunition, even if it be NATO milsurp, that you can buy and put into their rifle. Being that there's up to 80gr ammo out there, most leades are long. The guys at Savageshooters forum measured the leade on their .223 bolt actions, and it was longer than that of a Krieger barrel made for AR-15 rifles. And those Highpower guys that use Kriegers fire some ridiculously hot loads with heavy bullets. While there are warnings, and you should follow them - the safety margin has been built in already. They aren't going to leave it up to you. But don't test it either.
It isn't all about the freebore and the leade. There is also the throat (which is the width in that area). If that is tightened up, accuracy can increase quite a bit since the case/bullet will seat more concentrically. The fellow at AR15barrels.com tightens up the throat. Here's more info:
http://www.ar15barrels.com/forming.shtml
If you look at that link at the top of the post, the Krieger has the same freebore as the Bushmaster, but has a much more drastic leade. That is, the bullet is squeezed into the lands more rapidly. Due to being shorter. This makes the jump before being fully engaged in the rifling shorter. Thus more accurate since it will not get as out of line before the transition is complete. Kriegers are usually bought and used by people are are not newbies. Since to get any advantage out of such a match-grade barrel, you MUST use match-grade ammo. Most people handload, since match-grade ammo is very expensive. People who do all that demand more accuracy and aren't as likely to do something incredibly stupid (it happens though). So, these are pretty tight barrels for an autoloader for accuracy demands.
The more centered the bullet enters the bore, the less it will wobble in flight - the more accurate it will be. There are also other factors. Like distortion to the bullet etc.... Hard core benchrest guys make a huge fuss about their handloads, because their setups are so tight and precise, that how well centered the bullet is in the case makes a huge difference. If that is out of line, then it will negate the precision of the action and barrel.
I've found that the typical NATO chambered rifle, with decent ammo (like 75gr match) free floated, scoped, and decent trigger like an RRA 2-stage, will do around 1.25"-1.5" ..that's phenominal for a military pattern rifle with a regular barrel. Remember, in the world of guns, as you climb up the ladder of performance, the price doubles each rung. Want to shave .5" off those groups to have a 1moa or sub-moa rifle? Now you're going to pay 2.5x more for a barrel. No question about it. Standard rifle? 2-3moa. To get consistently under 2" usually around 1.5 to just under, spend on FF tube, match ammo, trigger ...want to get into the 1" ball park or under? Hundreds more on a super-match barrel....There are people who might say "what are you talking about, my off the shelf RRA will do sub-moa every day, even in the rain!" ...When I speak of accuracy, I'm referring to the rifle's ability to be able to do it CONSISTENTLY. None of this "group of the day/week/month" nonsense. Or 3-shot group stuff. 5-7shots or more, over and over. That's what a rifle can do. Shoot multiple 10shot groups, as slowly as you want, and you'll see that most of these 1moa rifles become 2moa rifles real fast.
