I had the same experience with my .308 Win. It normally shoots 1-1.5" groups at 100 yds. With the Hornady 150 Light Mags. it shot 4-6" groups. I couldn' t belive it. At first I thought something had come loose on my gun, but I checked it and shot another brand of ammo through it, and it shot just fine. I thought this was just an example of a particular gun not liking a particular load, but if this happened with three of your guns as well, it makes me wonder.