Then scope crossover is also a figment of peoples imagination, and it matters not at all if the dovetail lines up with the barrel, or if the scope sits above the barrel or off to one side ?
Neil.
Like I said, "If the scope is sitting on top of the rifle". I haven't stumbled upon term "scope crossover" before, but found this explanation:
Is this a symptom of ? - www.ShootForum.com
"Its when the scope centre is not aligned (left to right) directly above the bore centre."
I'll reiterate: if the scope is sitting on top of the rifle, that is, when you're taking the shot(s) the scope's longitudinal axis is vertically on top of the bore's longitudinal axis, the horizontal POI will not differ depending on distance (in reality it will drift depending on some minor ballistics which are generally proportional to time of flight, like spin drift which means right hand twist will cause the POI to drift right, but this is so miniscule at 100y that you cannot measure it).
If the dovetail is not in line (parallel) to the bore, you're using scope adjustments to bring the scope's real (internal) longitudinal axis parallel to the bore. If you can get the POA and POI to horizontally coincide at some zeroing distance, you've accomplished this. Other possibility is you run out of adjustment. Some scope rings have horizontal/windage adjustment just for this purpose (there was also scopes that had only vertical/elevation adjustment).
If the dovetail is in line but to the right or left of the bore line (when rifle is vertical and pointing downrange) the "scope crossover" will occur. Also if scope rings are not designed and/or machined properly, or if you're using rings which are designed for different dovetail width, the scope would not sit on top of the bore when rifle is vertical and pointing downrange. At this point the equation is simple geometry; if you're zeroed at 50y and shooting for 100y, the horizontal difference in POI will be the same as the difference in dovetail/bore position. A millimeter or two is actually quite big a difference and you'd be hard pressed to be able to measure a 5mm difference in POI.
You can eliminate the "scope crossover" by canting the rifle so that the dovetail (and scope) is brought directly on top of the bore, and then canting the scope so that it's level. But I wouldn't bother since the gains are minimal or non-existent.
So given you had POI differ 2 feet, I'd be inclined to search the cause from somewhere else. Like in the article I referred to, I only browsed through first page but on the post #9 the OP was already right on the money concerning the "scope crossover".