I find it interesting that nowhere does the OP state what caliber, bullet, rifle make and model, scope make and model and the automatic consensus is parallax due to one guy stringing and the next shooter shotgunning. I can think of a bunch more variables to throw in from shooter to shooter than parallax.
Me too. One factor may simply be that there's too few groups to draw any particularly meaningful conclusions.
The issue with parallax that I see is that any error attributable to it, on the given facts, is likely to be small. If we take it that the rifle shoots well at 100 it seems likely that parallax isn't an issue at that distance. If it is more or less parallax-free at 100 then the maximum error attributable to parallax at 200 is about 1/2 the diameter of the objective lens, for an eye at the extreme edge of the exit pupil. That is about 0.4 moa maximum, for a 40mm objective lens. If we allow for a shooter whose eye position is so inconsistent that they go from one extreme edge of the exit pupil to the other between shots we could add up to 0.8 moa. That is the extreme case though, and would be a technique issue at least as much as a scope issue.
It may be a factor, I guess. I suspect that it isn't the whole story, nor is it the only possibility.
