There is no lack of instructions online for marshmallow shooters (guns). However, we chose to use the one at Wiki How. The 12 steps and supply list are easy for builders of all levels. Our favorite volunteer, Mr. Whitright, priced materials online at a couple of box stores. Then we started brainstorming what sizes we might need to launch ping pong balls instead. Unfortunately our school has a strict $25.00 reimbursement limit, so I ended up with the suggested 1/2" diameter supplies. I bought four 10' pipes, a bag of ten caps, a bag of ten elbow joints, a bag of ten T joints, and a pipe cutter for exactly $25.00 at Lowe's. Store brand mini-marshmallows were under $2.00. Students got creative with designs, and even took guns apart frequently to accommodate new builders. The one in this photo has an ammo tube for rapid fire. HINT: Leaving the marshmallows exposed to air for 24 hours helps!