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Message: <blockquote data-quote="OPTIC_NUT" data-source="post: 3166878" data-attributes="member: 121951">A little more recent background  (than Hook):Phenomenon of the 'cell', associated with astronomical 'seeing':<a href="http://en.wikipedia.org/wiki/Astronomical_seeing" target="_blank">http://en.wikipedia.org/wiki/Astronomical_seeing</a>  (turbulent layer, pertrubed wavefronts, r0 and t0, FWHM, )<a href="http://www.wwnorton.com/college/astronomy/astro21/sandt/seeing.html" target="_blank">http://www.wwnorton.com/college/astronomy/astro21/sandt/seeing.html</a>   (can even happen with 0.1C difference in large scope barrel, but happens over miles of atmosphere)("seeing cells,"....eddy lenses....millimeters to...meters wide..."swarm" in the sky)---------------------------------The geometry:---take two tubes, 2 feet apart on center, and a 2 degree field of view---at 100 yards, two feet is  arctan(2/300) = 0.38 degrees---but....for EACH barrel, that is about 0.2 degrees to the common centerline    (note that I am going "3 axis", as it were)So.....if the fov is 2 degrees, and the two sides are truly parallel   1.8 degrees of the 2.0 degrees is already FULLY OVERLAPPED at 100 yards.   So...long before that you will not have seperate 'cells' for the two sides.   Maybe it will help with your barrels at first, but you should have left them to cool before you looked.That's what I'm talking about. It is what it is.</blockquote>