I cannot back it up with any reports, but I still have to think that the asymmetrical receiver mass could well have some harmonic effect upon the horizontal component of the impact point, especially on the LONG rifle barrel. We KNOW the left drift to be "wrong" as it contradicts all other testing - and, the fact that it self-corrects at extreme range only supports that fact.

I do not know how the firing was conducted. Single-loaded? Possibly, but likely not. With box and follower, etc. removed? I sincerely doubt that. Consider the weight of the box, the follower, and two cartridges, and their moment arms from centerline. Yes, the side-plate has mass too, but the receiver is still right-side heavy (and right side stiffer) to some degree, all of the time. The relative effect would be much less in the carbine of course.

It is my understanding that the extra notches on the 1898 sight were mainly to provide a crude lead for moving targets, not for drift correction, even though they are not spaced equally off-center.