Typically when "overbore" comes up, it's applies to rifle cartridges, such as the 243 Winchester, 270 Winchester, 7mm Mag, etc. But not handgun rounds. Since, revolvers cartridges are the only handgun cartridges this could possibly apply to, I posted on the revolver forum.
BTW:
BTW:
“I have read countless discussions about overbore cartridges for years. There seemed to be some widely accepted, general rules of thumb as to what makes a case ‘overbore’. In the simplest terms, a very big case pushing a relatively small diameter bullet is acknowledged as the classic overbore design. But it’s not just large powder capacity that creates an overbore situation — it is the relationship between powder capacity and barrel bore diameter. Looking at those two factors, we can express the ‘Overbore Index’ as a mathematical formula — the case capacity in grains of water divided by the area (in square inches) of the bore cross-section. This gives us an Index which lets us compare various cartridge designs.”
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