But Ray Ordorica looked into that. He found that his double, I forget the make, shot parallel. His individual barrel groups remained that inch apart as far as he could get good hits.
I have long read about doubles - especially double express rifles - being regulated to converge both barrels to the same POI at some arbitrary range.
I've read that kind of thing, too. Its's not quite correct.
Close POI, relative to the POA, but they aren't trying to put both shots in one hole ON the point of aim.
Double rifles are regulated so that each barrel's bullet strikes within "x" amount of distance from the point of aim at a given range.
Its a small detail and is often overlooked, or not mentioned. And most readers will assume the intent is to have both shots hit the exact same point.
Reality is, a bit different. There is no, and I doubt ever was any serious attempt to get both barrels to his exactly the same point. The point always was to get both barrels to shoot the same, relative to the point of aim, and close enough to it, and each other to do the job the gun is built to do.
Meaning, (for example) at your chosen distance, if the right barrel hits 2" off from the point of aim, the left barrel should do the same (or less). It can, and normally is in a different direction from the other barrel's hit, but it needs to be within the desired distance, this gives you a "group size".
Both barrels need to be about the same in their divergence from the point of aim. That's what regulating them does. Rt barrel 2" off, left barrel 2" off, ok. Rt barrel 2", left barrel 8" off, not good enough.
Remember what the primary objective is. The rifle must group (both barrel) well enough, absolute perfection is not needed. And not sought, as it is a waste of time, effort, and money.
When the required minimum is "minute of charging water buffalo" you're going to build guns that do that, or a bit better.
Whether it is done the old way, with soldering, test firing, adjustment, test firing, etc or done with laser pointers or done by just aligning the barrels in a fixture during assembly, it is still done. It is the end result that matters most.