I'll be the first to admit that I sometimes get horrizontal stringing with my heavy kickers after I've had too much of them....I'll jerk the trigger etc. I shoot left handed and most of the time pull them off to the left...Now take the human error out of the equation and just focus on the mechanicals, a horizontal stringing issue is usually a result of uneven barrel contact or pressure on one side (the reason many suggest freefloating to accurize). Poor bedding can also cause horrizontal and vertical stringing. None of my rifles are left unbedded, so that is never an issue. However, I've seen it and fixed a few of my friends' rifles with issues...
