I asked this on another forum but I wanted to know what you guys recommend. I am wanting to build an AR-15 SBR. I am trying to figure out what the best caliber would be to meet my needs. I am looking for something that would have effective terminal ballistics from CQB range out to about 150 yards. I was thinking about going with a 10.5" barrel. I am not dead set on that barrel length though. I will be reloading so wildcats are doable. What say you?