Blast It

I should've realized that you can't necessarily fit all the explosive inside the grenade. 30 grams of ONC has a volume of 14,563.11 cubic millimeters, whereas the "based on shotgun slug" grenade-design I was using only has a volume of 5,282.41 cubic millimeters—the HEDP round would need to be 2.76 times the volume of the slug. The 20.71 grams of ONC for the air-burst one, meanwhile, has a volume of 10,053.4 cubic millimeters, a volume 1.9 times that of the slug.

All is not lost; a polymer-cased grenade is presumably much less dense than a slug. (I find, incidentally, that the slug in question, given its mass and volume, has roughly the density of thulium, 9.33 g/cm³. It's also the density of the molybdenum-alloy "mandrels" used for piercing stainless steel tubes, so, maybe they're made of that, for improved armor-piercing characteristics?) If we wanted to make the HEDP round work the same, it just has to be 62.83 millimeters long, or about as long as a modern 3" shotgun shell (remember, shotgun shells' actual length is about half an inch shorter than their listed length); the air-burst round has to be 43.25 millimeters long, or about as long as a 2.25" shell.

One thing this probably means is that, while they can load tubular magazines with any combination of shot, slugs, and grenades they feel like, they have to load box magazines with all the same thing. (Actually if the 1.75" Aguila "minishell" is any indication, they may have to load their tube-magazines with all one thing too, or else have some mechanism to vary the "size" of the motion in the feed mechanism. Apparently the minishells have feeding problems in many guns.)