Just curious. Some mfg can have between 1/2 to 3/4" difference in the distance between the rings depending upon how you screw in the bases. If there are no cartridge loading or tube length issues, is there any mechanical advantage of wide vs narrow? Specifically for QD rings and large bore thumpers?

With the assumption that a scope body doesn't flex I can't see how spacing would be an issue.

Other than personal choice and what looks good.

It would seem to me that a wider ring placement could give somewhat better scope support than a narrower one, at least in theory.

Not sure that 1/2 to 3/4 inch would make much difference, but placing the forward ring on the barrel, instead on on the receiver ring, for example, might help to reduce the leverage that a blow to the objective end of the scope could produce.

And the same for the ocular end, although there is usually not much latitude in ring placement there, at least not on a bolt gun with a top mount.

For that reason, I always try to keep the scope rings as far apart as possible on my rifles, although often there is little choice.

To the extent that there may be some misalignment in height in the mounts, the longer spacing will minimize this error. But so will a couple of thicknesses of electrical tape between the scope and the ring, so the longer spacing is not of much significance.

It is also true that the scope has less leverage on the longer spacing, but any reasonable spacing provides ample stability, anyway.

Wider is better from a mechanical leverage perspective, but from a practical one; don't worry about it. Just shoot it.

I wonder about those scopes on double rifles with the mounts close together and a great heap hanging out the back. And considering the right-left abuse recoil must wreak on the internals of scopes on s/s doubles, I'd be surprised if any modern scope could stay zeroed in long enough for the clockwork to seize up they way it used to on old ones.

On another tack, Unertl et al used to want their target scopes set up with mounts 7.2 inches apart in order for the external adjustments to give neat quarter-minute clicks. That is a fair distance but some of the scopes were a foot-and-a-half long.

I have doubles with some very close ring spacing, and heavy recoil. They work fine even though they look like they will fail. And they return to zero. Modern scopes are pretty tough pieces of hardware. I still like them as far apart as possible, but sometimes it ain't.