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Old April 11, 2011, 10:23 AM   #1
Join Date: January 7, 2011
Posts: 28
Bore sighting

Bought a new Bushmaster AR, put a redfield 3x9-40 scope on it, bought a laser bore sight tool that fits in the end of the barrel. I don't have the ability at home to check it at 100 yards so I did it at 25 feet. The kit came with a chart to use to check at close range but did not say how close. Basically you compensate for the distance from the height of the red dot to the center of the scope, but as I said it does not say what distance to use if you do it this way. Any recommendations?

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Old April 11, 2011, 11:12 AM   #2
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I'm not sure about a laser bore sight device, never used one. I'm still of the old-fashioned school of "look through the bore and adjust your sights to what you see"

A boresight is only good for getting on paper, anyway. Anything you find with the tool has to be confirmed at the range.
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Old April 11, 2011, 11:17 AM   #3
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The answer varies with how high the centerline of the scope is above the bore line and how flat the load shoots. If I put in a 55 grain military FMJ and in the range of 2800 to 3200 fps MV, then for 100 yard zero I expect the dot to be below the crosshairs by about:

Dot 7/8" below where the crosshairs look for sight centerline 1" above bore line
Dot 1" low for sight centerline 1 1/4" above bore line
Dot 1 3/16" low for sight centerline 1 1/2" above bore line
Dot 1 1/2" low for sight centerline 1 3/4" above bore line
Dot 1 11/16" low for sight centerline 2" above bore line

You could go inbetween the numbers for whatever sight and bore centerline distance you actually have. You can't really expect great precision by this sighting method. If you get a laser bore sighter to put you within 3" or 4" at 100 yards, you've done about all you can expect anyway. Still, it gets you on paper, so you're ahead on sighting shots required to find final zero.
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