[edwin hubble]

"Why use a 122? What's wrong with the 4duce?"

The 122mm is half again the projectile size of the 4.2 inch.
the 122mm range is 8.2km vs. a range of 5.4km for the 4.2 inch.

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The 4.2" mortar is 106.68mm in diameter, compared to the 122mm mortar. (a ratio of 1.1436 to 1)

If you compare the relative volumes (taking the cube of the diameters to approximate the mass and volume of the projectile) it is 1.50 to 1.

[fourdeuce82d]

If you compare the relative volumes (taking the cube of the diameters to approximate the mass and volume of the projectile) it is 1.50 to 1.

Impeccable reasoning & calculation...shot down by an inconsiderate reality! *grin*

it would seem like that should be the case, but it's not- the 120 mm rounds are about 30 lbs, the 4.2" are ~26. The thing is, the two rounds are shaped differently- the 120s taper back to a fin assembly, whereas the 107/4.2" rounds look like artillery rounds with a small tube sticking out the bottom to hold the "cheese charge" propellant.

IIRC, some 120mm rounds actually have less explosive filler than the 'deuce. But the greater diameter of the 120s, plus their lack of spin, would be an advantage if you wanted to use them to deliver a shaped charge warhead.