i don't wish to take this thread farther off topic, but it seems a reasonable place to pose a question that i have wondered about....
is there any concrete evidence re: the effect tighter (or looser) than normal bore sizes have on pressure levels? we see guns with 13, 13/1, 12, 12/1 markings...as small as .710 and as large as .740. that's 30 thou difference between a "tight" 12, and a "loose" 12.
i have recently gotten the MF Ideal with the shallowly rifled right side tube. it was proofed at .716, and measures that in the lands, and about .726-7 in the grooves (not easily measured). i'm far away from attempting to shoot the barrel with a slug, but it has given me an interesting question to ponder. every commercial slug i've seen specs on has been somewhere in the area of .736. that's 7 thou to swage down on the small driving bands typical on the modern slugs...if you are .729 in the bore. but if you start out 8-10-12 thou smaller...the swaging effect is how much greater? then, i started to think about pressure differences of normal one piece wads working through tighter/looser bores.
i seem to recall burrard's book mentioning something about his preferred felt wads sealing forcing cones and bores better than hard card types. but that far predates the modern plastic wads. sherman bell's interesting experiments in DGJ mention pressure differences between tight and loose chambers, but i don't see anything related to bore size variations.
the only other reference point i see is the obvious strong correlation between oversize bullets and higher pressures in rifles. has there been any work that considers this factor in shotguns?
