Heh. Always one to jump in with a military reference, I feel compelled to note that this term was also World War II-era slang (I'm not sure in which armies). It referred to the German standard-issue thrown grenade, which consisted of a ring-shaped charge with a short stick through the middle, the charge resting at one end of the stick. This design allowed soldiers to either lob the armed grenade, stick and all, or for greater range, they could 'whip' the stick forward, causing the charge to slide off the end and continue forward. The extension of the soldier's throwing arm, by the length of the stick, caused the grenade to move more quickly and hence fly farther.

Having read the above w/u, I surmise that the notion of a mortar-like stick embedded in a bowl-like grenade led to the comparison.