I wonder about doubles only shooting well at a particular range.

Forsyth wrote "THAT" was W. Greener's premise in 1858, that a double gun could only be made to shoot well at an exact range. He also stated that it would cross at all further ranges due to the inclination of the barrels. Forsyth then wrote he believed that if the barrels shot perfectly, ie: the gun was regulated to shoot parallel, the bullets or balls would be parallel at ALL ranges.

He stated he'd owned 2 that shot perfectly and proved such shooting by shooting through paper at ranges out to 100yards, where at every 10 yards paper, the balls (grouping) were still hitting parallel. W.W. Greener, in 1911, IIRC from his writing, agreed with the perfect regulation as being parallel.

I do not think it out of line to attempt to find a load that shoots 'perfectly' - ie: parallel - even though for hunting purposes, that is not necessary and slight allowances can be made for the size of the 'X' ring.