I have a thread in a different area related to this, but this aspect of it is probably more suited to this forum.

Long story short, when bullets are unstable (via rpm), do they typically strike a target (say at 25yd) and make the same general sized holes in the same general orientation? I.e. when bullets are unstable, are they consistently unstable assuming consistent ammunition/velocity?

I've seen plenty of keyhole targets where the bullets are all over the map, but I've got an issue where I have only a slight wobble. However, the impacts on my target are roughly the same "size" oval and are making these ovals in roughly the same "direction". In other words, the bullet appears to have entered at the 3 o clock position on the oval, and the whole oval is oriented horizontally on the target. This is repeatable.

This is a factory firearm with two factory ammunitions.

When bullets are slightly unstable, do they impact in the same way or is it generally random? Can muzzle blast or the shape of a muzzle device have a considerable impact on bullet stability (assuming nothing is touching)?

The direction the nose is pointing can safely be said to be approaching or totally perpendicular to the direction of travel once they go ass over tea kettle. You can't predict the direction the nose is pointing very exactly other than it won't likely be directly at or directly away from the target but the direction it is pointing is not entirely predictable other than that.

Are you sure they're wobbling? What's the calculated Sg? Is your conclusion based only on holes in paper? Do you see divergence/convergence effects as range increases?

Bullets that are not fully stablized enough can precess or nutate which could in theory cause oblong holes but if it was a big enough effect to see in the paper I would expect keyholes shortly thereafter. Combustion gasses outside of the muzzle can have an effect but probably not a large enough effect to cause what you're seeing without the bullet already being unstable enough to go ass over tea kettle.