I always use to sight my rifles @ 100, was told thats the way you gotta do it. But lately i have been zeroing at 25, and I mean exactly zero, and then checking at 100 or 200. And surprise surprise the last 3 rifles have taken me either 7 or 8 rounds to get it right - 2 at 25 and then a 5 shot group at 100 to check zero and group. And all have been exactly where I want them, either 2.5 or 3.5" high depending on calibre and speed. So yes it is possible to get it right at 25, but definitely check it at 100 or 200 as soon as you have the opportunity.
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