Kudae,

True it is somewhat a theoretical discussion. As the variables often make it true in theory but only approximate in practice. Actually it is the reason I titled this thread "Internet absolute", because the theoretical ideal is usually stated as a fact or "absolute". Only on the internet ...

Of course you are correct with your description on how the barrels with increasing distance will form composite figure 8 like groups. One reason I think for longer range shooting, a DR could better be thought of as a single shot, with a second barrel attached to it. I think if one barrel, the first is more accurately aligned to the sights, with the second barrel regulated to be as close as reasonable, one has a rifle which can be used at longer ranges (ie medium ranges) where a second barrel is fine for closer shots, quick follow ups etc, running shots etc. Often where other variables all come into play as well.

Purists often disagree with that sort of thinking too.

My only personal "regulation" is with my Valmet/Tikka barrels. As you know, they have separated barrels, with adjustable wedges. Also under and over configuration. Interesting though my 9.3mm barrels will shoot from each barrel pretty much one hole, or clover leaf 1 inch or sub-MOA groups (2 or 3 shots from each barrel) at 100 metres. I try to get it shooting each small group about three-quarters of an inch apart at 100 metres. In theory the top barrel should be as accurate as any single shot or bolt action at longer ranges.

Though regarding accuracy, the very first double rifle I ever shot (1983) was a Frankonia U/O in .22 Magnum and 5.6x50mm Rimmed. The 5.6mm shot three shot one hole groups at 100 metres consistently. Even with the horrible stocking, very high mounted scope etc. I have no idea/recollection of that rifles regulation except we were happy where it shot at 100 metres.

Good you have brought up the human dynamics of regulation. That the barrels are not parallel, I don't think anyone has claimed them to be. And that the angle barrels face each other actually must compensate for the initial recoil of the rifle (especially for larger bores), the time the bullet is still in the barrel during recoil moving the point of impact apart. One reason human regulators are used, trial and error, not a computer programme. And a big reason for the higher cost of DRs actually delivered regulated.

I don't pretend to be a gunmaker in the slightest, nor even a very technical person with regard to these fine guns, always have said more of a user of them. But on these forums, I think a lot of guys LIKE to know at least the basics of the theory, out of interest. If not more. Otherwise we would not bother discussing them here on forums at all.

Good to see the responses and participation with comments.