Re: I\'ll bet somebody knows the answer to this.
As stated above, vertical stringing can be caused by a need to vary the powder charge, too much variance in your charges in any given string, or, could be due to an inconsistency in return to battery. With horizontal strings, it's usually wind or a heavy trigger, or, possibly, bedding. If you are getting a tight group with a triangular pattern, bbl harmonics are at play and you should vary your charge up and down 1/2gr at a time until you hit the sweet spot. Good luck.