I have a .270 left A bolt. It will shoot sub MOA with factory winchester ammo. Browning's web site has a list of where to start with the calibration of the BOSS. I would start there. It shoot very good at that setting. One caution though. Do not allow the BOSS to loosen up. A loose BOSS will change the POI a ton. I ran some high energy ammo through the gun and the boss loosened up(I dont know why). The next time I shot I did not realize the BOSS was loose and my POI was a foot high and 8" right. Keep an eye on the BOSS and you will love it.