I understand that Charlie Sisk developed his guidlines because he found that most of his customers won't spend much time developing loads. But a properly put together light, even a light, long, whippy barrel will shoot at least some loads quite well. Just not nearly as many as a much stiffer one. My 24 inch, Lt. Mtn. Pac-Nor has, and does, shoot some ammo into .5, even a few times down to .2-.3 MOA. But not nearly as many as my #1 contour barreled rifles.
The two most important things in building a light mountain rifle are (1) make sure all of the pieces make your weight goals, and (2) make sure that rifle doesn't end up muzzle light. I prefer it balance on the front reciever ring.
Any top quality barrel, properly installed, should shoot at least a few loads plenty good enough for a light big game rifle. E
