I've always liked "firestick," "bangstick," "smokepole," "Hand Cannon," and "Bullet Hose."
My two guns have their own special names:
My Ithaca M49 .22: "Karait" after the small brown poisonous dust snake in Rikki-Tikki-Tavi by Rudyard Kipling
And my J.C. Higgins M20 12 gauge: "El Viejo" The Old Man in Spanish, which is appropriate, considering that gun is a few years older than my dad, and forty something years older than me...