I have a Stevens 200 in 223, factory stock, and it is an awesome rifle for that distance. I routinely ring the top of a "T" post at a measured 180 yards from a rest. As far as barrel length, I find the shorter 20" barrel performs extremely well. I have 223's in 14" (Contender pistol) 16" (AR Style Rifle) 20" and 26". There is little difference in accuracy vs barrel length in my experience. Also not a huge difference in velocity. I would guess that you could experiment with a slower powder in the 26" and maybe get some more velocity out of it, but the 223 is already cranking out there where I need it to be. Try out a factory stock rifle before you spend a lot of money up grading it. (Unless you get a really bad trigger like the Stevens 200 I just bought and upgraded in 300 win mag) You may be surprised at how well you shoot it.