Article: This should be soft enough that you can cut a slit through it with a flathead screwdriver. Get several, if you can, in case you mess up your first try. Put the bottlecap down on the table, with its top upward. Stick a flathead screwdriver through the vertical side, under the bottlecap, and through the other side. This pair of holes should be very close to the lower rim. Make the holes wide enough to fit a popsicle stick. Rotate the cap 90º. The holes will now be on the left and right. The side in front of you will have no holes in it. Push the screwdriver through in this direction to make holes at a 90º angle to the others. These holes will be halfway up the cap's sides. Leave room below and above them. These should also be wide enough to fit a popsicle stick. One popsicle stick goes through the two lowest holes, just poking out one end. A second stick goes through the middle holes, poking out equally on each sides. Now you have a † shape through the bottle cap. Keep the cap pointed the same direction. Poke the screwdriver high up on the sides, near the flat top. Make these holes small, and keep them straight over the lower stick. You can use a larger, Philips head screwdriver to make the holes round without making them wider. Take a wide rubber band. Place it over the bottle cap, above the sticks. Hold it against the top of the †. Pull the lower end over the left arm, then the right. Repeat until the rubber band is mostly tight. Pull the rubber band down over the top of the bottlecap. Take the cotton off one end of a cotton swab. Stick the swab through the top pair of holes, starting at the top of the †. Pull back on the rubber band and let go to fire.  If the rubber band doesn't pull far enough, unwrap it once from the arms. If the cotton swab won't fit (without the cotton ball end), make the hole larger with a screwdriver. Pull the rubber band back as far as it can easily go. Mark that spot on the stick with a pen. Push a thumbtack just in front of that spot. You can now keep the rubber band "locked" by stretching it over the thumbtack. To shoot, pull out the tack or pull up the rubber band and let go. The rubber band will wear out fast if you keep it locked. Unhook the band any time you aren't using the crossbow.

What is a summary?
Find a plastic bottlecap. Poke a pair of holes near the rim. Turn the bottlecap. Poke a second pair of holes. Fit popsicle sticks through the holes. Make smaller holes. Fasten with a rubber band. Load the crossbow. Add a lock.