Hoppered HAMPs are manually driven, semi-automatic blasters that can be easily built with minimal tools for under $20. The power is partly a function of how hard you pull the plunger, so you can only use as much power as you need. As described here, a casual stroke will fire a 1 gram dart ~150 fps and a very hard stroke ~200 fps, but longer or shorter barrels can be used to increase or decrease the power of these sort of blasters. EYE PROTECTION IS MANDATORY FOR ALL PARTICIPANTS WHEN USING THESE TOYS!
These instructions mostly explain how to make these for special hopper-friendly nerf-like ammo that is difficult for many people to make or obtain. However they can be used to produce a semi-automatic marshmallow shotgun that uses extremely cheap and ubiquitous mini-marshmallows. There are some additional things you should know if you are going to do this.
If you're going to use these for marshmallows, there are a few differences in design and operation.
-If they get too melty they will get unremovable gook all over your barrel that will prevent it from working again.
-If they get too cold, they will be much less soft, which leads to both more target pain and fewer projectiles fed per shot.
-Stale marshmallows act like cold marshmallows. They get stale fast.
-You CAN use an easy-to-find Tee fitting instead of the wye fitting.
-Use 1/2" Thinwall pipe for the magazine. It should have an ID of nearly 3/4", but still fit in 1/2" pvc fittings.
-If you can't get 1/2" thinwall pipe, try to find something with close to 3/4" ID, and just improvise at the coupler point. Probably lots of duct tape, and you will have to reload from the cap.
-Try sch40 1/2" PVC if you feel the barrel is too tight for your marshmallows. Sch80 is usually good for most mini-marshmallows.
-If the marshmallows aren't feeding enough, you can use a follower. For example, a 4" long stick 1/2" round of nylon cannot reasonably be forced through the wye, but will push on the marshmallows in the magazine if placed on top of them. This makes reloading more of a hassle, but will usually result in more reliable and impressive blasts of marshmallows. Just make absolutely sure that the follower can't be fired.
-The amount of marshmallows fired in such a short amount of time can make cleanup taxing, depending on the environment. Ideally find a place where they can all be swept up, or a place where they don't need to be removed from.
Also, if you want a blaster that works with actual Nerf darts, there is a simpler frontloaded version of this blaster. Instructions for that are here: https://sites.google.com/site/mostlyharmlessarms/c...
Information about the ammo can be found here: https://sites.google.com/site/mostlyharmlessarms/d...