I agree with Steve.
: A realistic possibliity for a load that shoots only 1.32" at 50 yards might be closer to 10" to 12" at 200. As Steve said, 1.32" at 50 yards is not a good group for such a close range.
: Merely doubling and doubling the initial group size just doesn't work in the real world. It is a mathematical equation, not a reliable indicator of a load's possibilties, as longer ranges allow bullet stability and suseptability to the elements to enter the equation.
: As KDM noted, the open grouping may due to open sighs that are close together and having no definite aiming point.
: Proper targets are necessary for shooting groups and perhaps they will rectify that in the near future.
: As an expample, my .458 shoots sub 3/4" at 100 meters with jacketed and 1" and just under 1" with 505gr. cast bullets. It has a 2X Leupold on it. At 200yards, I get 3" to 3.5" groups, much larger than double the 100 yard grouping. Doubling a short range group just doesn't pan out.
: As far as the rifling is concerned, most .458's have 14 to 16" twists and will handle bullets to 700gr.fairly easily. I suspect the grouping is due to the test method as indicated by the shooter.
: 1.32" is only .2" tighter than my 1911 Colt, Wilson barrel provided with 260gr. Speers. Does that mean it will hold 6" at 200 yards?