I can offer match barrels from Shilen and now McGowen. Both will have 223 Wylde chambers and with good quality bores, should shoot very well. Other chambers may be possible.
McGowen can come complete with the barrel extension installed. Min is 16". Max is whatever you want.
Likely the cost of a prefit is less then a blank, contouring and install. Plus you have the advantage of a prefit to have the barrel stress relieved after contouring.
CM can be blued. SS cannot. Either shoot well, CM is always less money and some say more durable. I have shot them both in bolt rifles and equal quality barrels shoot with the same level of performance.
Barrel length has more to do with velocity then accuracy. Pushing a match bullet as fast as possible will help with LR ballistics.
In a 223, 20" is a min for getting as much out of the case as possible. 26" is ideal. Of course, that is not normal fare in an AR so 18 and 20" are nice compromises.
If your goal is sustained accuracy over a clip or two, best to go with a heavier contour barrel. There are a number made popular by Camp Perry style shooting. They will still accept conventional accessories but the extra ' meat' keep the barrels from warping thus shooting their best.
Properly stress relieved barrels will help alot in this regard. I am unfamiliar with some of the AR specific brands but the quality barrels from the target shooting world are all stress relieved.
Fluting is more cosmetic then accuracy enhancing. About the only thing it does do is reduce the mass of the barrel. However, proper contouring will do the same job and not run the risk of inducing stress in the barrel.
If only shooting 55's, 12 twist is all you need BUT I would still suggest a 9 so that you can run common ammo later. The 55's will not care about going through a 9 twist.
The big issue to getting the most from any rifle is the chamber and how it is shaped to the ammo shot. If your goal is to get the most out of light weight bullets, chambering in a standard 223 SAAMI chamber will be the best.
However, the shorter throat will raise pressure issues if you decide to run NATO ammo with heavier bullets.
Chambers like the Wylde have longer throats but not as long as the NATO 5.56 so many shooters are getting excellent accuracy AND proper functioning. It definitely suits the heavier slugs but is likely on the long side for the light bullets.
If you can handload, you will be miles ahead as you can tune the ammo/bullet to the barrel harmonics for best performance AND you can use a shorter throat to maximize accuracy.
Jerry
