This is my HAMP. It is a really awesome type of homemade blaster that doesn't even require a spring.
I added some dart holders to it to make things more convenient. I'm using a 1/2" PVC barrel for it. CPVC didn't work because it was too tight of a fit. PVC works just fine with taggers, sonic micros, and streamlines. Taggers and micros work the best though.
I added a stop made of dowel rod to it so that I don't knock the back off of the whole blaster. The key ring can go on the rod to stop the plunger from falling forward which I really like. I might get around to making an RSCB for it but i'm not sure if I will. I made this blaster purely for fun and I don't plan on using it in any mini wars that I have. I really like how it turned out.