A four inch penetration in the back, or front is nothing to sneer at.
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Depending on the build, and where in the back it hit, four inches could reach the lungs, from the back, destroy a kidney, or other organs, and paralyze from the entry wound down,etc.
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I would guess he used a target point, and not target field point, the ones that taper to a point. Good thing it was not a broad head.
Or obsidian........
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Mr. Wood reminds me of the story of Paul Revere. ......a little light in the belfry........
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Wayne