Take your bottle and drill a small hole in the bottom. Make sure it is big enough for a flame to go in.
Step 2: Step 2
take your barrel and attach it to the bottle using duct tape. Make sure its snug and cant move.
Step 3: Step three
Take your ammo and put it down the barrel (cotton balls are fun). Then spray some flamable of your choice into the little hole, wipe off the liquid that gets on the outside.THis will cause the plastic to catch on fire. Then lite it and bam your 1 minute gun.