A wizard or sorcerer with False Focus casts Fabricate Bullets to create Colossal-sized firearm bullets for free. He then carries them in a bag or Handy Haversack.
The spell makes bullets from 1 pound of lead there are no collosal bullets there:(
Edit: and since you need both 1 pound of lead as material and another to transform as the spells target it wont even be for free. Not a well written spell.