50. Cal Sniper Rifle can take out tBoC easily due to range and penetration capabilities. You just need to worry about not dislocating your shoulder --- You will never forget this Devil's power. You are not worthy as my opponent.- Vergil PSN-DevilNeverCry124. Go read the Dark Tower Series by Stephen King!
Rocket Launcher, a portable one with lots of spare rockets could easily take down most of the bosses in Dark Souls. Stray Demon? 1 rocket from the ledge takes him out. Taurus? Shoot him out of midair a she jumps onto the bridge. Red Drake on bridge? Not so fire proof on the inside! Bell gargoyles etc etc.