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Getting back to the original posting, in answer to the question asked (would it be worthwhile to rifle the barrels in opposite directions for a double rifle), and speaking as a barrel maker and rifle smith:
If I were going to make a pair of barrels to furnish to Searcy, say, to have him make-up a DR for me (because I sure don't want to), I'd make the rifling of each barrel in opposite directions (because I can).
Do I think this would make the rifle shoot more accurately, or easier to regulate? No. But it appeals to my sense of symmetry, and a double rifle should be nothing if not symmetrical.
The real reason why DR barrels must be set to converge is, as I hinted, based in their geometry as an assembly in the rifle: the support given to the barrels (and the rifle as a unit) is not in-line with either bore. If the support to the barrel were truly in-line with the bore, the resulting recoil vector would also be in-line - straight to the rear. Since hunting rifles are built to be shot by human beings from the shoulder, the line of the bore nearly always lies above the midline of the rifle stock and its placement against the shoulder; the resulting recoil vector is upward and to the right (for a right-handed shooter - to the left for a southpaw). In a DR, additional force vectors are introduced by the barrels' positions off the centerline of the assembly, right for the right barrel and left for the left tube (in a superposed DR or shotgun, the barrels lie nearly on the vertical centerline, but at different distances from the center of rotation against the support, so the force vectors are more vertical, but not equal - the regulation problem is much the same, but the convergence/divergence problem with POA is primarily in the vertical plane).
In regulating the barrel pair to place shots from each barrel close together at some specific distance, the convergence of the barrels must be established by firing the assembled rifle with the appropriate ammunition at the desired range, and correcting the barrel pair's assembly until the desired result is achieved (and perfect coincidence is not necessary or realistically attainable). The procedures are well established, and obviously well enough understood by the experienced maker to achieve results which leave little to be desired in a practical sense. This process, while expensive and time-consuming, has never yet been, and is unlikely to be, superseded by any theoretically-based algorithm permitting the maker to assemble barrels (and rifles) which always shoot perfectly without further adjustment: there are too many variables in the rifle, ammunition and shooter to permit it - rifles are dynamic devices. Rules-of-thumb do work well enough to enable the maker to save some time by using a pre-determined amount of convergence in assembling the barrel pair before shooting begins.
As to the effect of rifling direction, per-se: barrels with right-hand pitch cause the bullet to drift to the right, and the barrel to counter-rotate to the left; the opposite being the case for left-hand pitch barrels. So, in a theoretical sense, if I were assembling opposite-pitch barrels in a side-by-side DR, I'd place the right-pitch barrel on the right (as a counter to the recoil force vectors), and the left-pitch barrel on the left. And remember that, if the barrels are set to cause shots to converge at some pre-set distance, they will, in theory. continue to cross at longer ranges - the drift will help compensate for this (in theory, and in the above case for opposite-pitch barrels). In reality, though, the forces introduced are so slight as to be, probably, insignificant, so far as making any real difference in the regulation process, and, as I said, there is nothing to be gained in accuracy.
I hope this will help clarify the point. But I doubt it. :->
mhb - Mike

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Sancho! My armor!

Edited by mhb (26/10/05 06:50 AM)