The size of a firearm's bore, known as its caliber, can be defined in terms of three different units.
- The largest of Alkenstar's siege weapons, such as the Great Maw of Rovagug, can be measured in 3-inch stones (S).
- The next smaller unit is ¼-inch pebble (P), with 12 pebbles to a stone.
- Finally, a pebble constitutes 24 grains (G), the smallest unit of ballistic bore measurement.
While many personal firearm bullets are 1P in size or greater, the grain is a more common unit of measure since few of them are an even pebble in size.
|Size in ...||S||P||G||Inch|
|Pebble (P)||0.083 1/12||1||24||0.25 1/4|
|Grain (G)||0.003472 1/288||0.0417 1/24||1||0.010417 1/96|