Howdy folks. I recently began work with my first ever long range rig, its a Zastava Mark X in 6.5-284, 27 3/4 inch benchmark barrel, fluted, leupold 6.5-20 on top of it, in a boyds laminate stock, actually a pretty sharp looking piece. Anyway, I have been doing all of my development at 350 yds, and have a horizontal stringing issue. all bullets land within about 1 to 1 1/2 inches of each other vertically speaking at that distance, but horizontal is more like 4 inches or so, Any advice on how to fix this? bedding maybe?, how would I check?

Thanks
Nick