Can you observe ANY difference in the appearance/location/orientation of the last round when in feed position, as opposed to any of the preceding cartridges in exactly the same place? Is the last round any more/less subject to wiggling with a finger? Is it more/less "loose" than any other? Some difference should be expected, as it is "held" differently than any other.

Perhaps a couple of carefully posed pictures? Speaking of which - some of the foregoing while very clear, do exhibit some pretty serious distortion - might be better to back the camera off a bit and then crop/enlarge the image.