[Chemist_Geek]

The gauge of a shotgun is the reciprocal of the weight (in ounces) of the shot used in that gun (?)

Not quite. We're talking about a single lead ball. Even the largest shot, 0 buck, has more than one pellet per shell. Slug shells aren't spherical projectiles.

The density of lead, I just looked up in the Alfa Aesar catalogue, is 11.34 g/cm³. The volume of a sphere is (4/3)*pi*(d/2)³. And, um, a pound is 0.454 kg. So, a 12 gauge shotgun will fit a ball which is 1/12th of a pound or 37.8 g, which based on the density given above has a volume of 3.34 cm³, or a diameter of 1.85 cm. (If I did the calculations right, it's only 8:30 AM here.)

[absalom01]

The math looks good, but you didn't convert to inches -- divide by 2.54 and you get .755 inches, which is spot on, even with two unit conversions.

This is true for all guages except the .410, which is not a guage, but a caliber. Given the way this thread is going, I'm sure someone can fill us in on the historical reasons for this -- I've heard plenty of lore, but not much in the way of fact on this point.

What a bunch of geeks!