I use to have trouble when I changed from field tips to Hunting points with flight right off the bow and would have to raise my nocking point or at least fool with it a bit to get the tail high out, I always had my head horizontal , I started mounting them vertical and the problem went away, I don't know,
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but figured it had something to do with wind plane as the bow was released, not sure but solved my problem so Vertical it is for me.
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don't think it matters much if flight is good ,the arrow is spinning inflight anyway. Heard and old saying, the Indians mounted there heads vertical for 4 legged critters and horizontal when hunting man, something to do with the rib cage
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but as I said they are spinning so that's out the window, but I thought a pretty cute saying.
Pappy