As far as blowing ones hand off, I can imagine a few scenarios that could cause that. However, it doesn't happen if you are careful and moderately intelligent in your build. Schedule 40 ABS is much better than PVC. When PVC breaks, it shatters, but ABS bends. In any case, pnuematic spud guns are the only real ones that have a chance of bursting on you, because they have a sustained pressure while combustion guns are a fraction of a second, and the pressure will take the path of least resistance, always through the potato and out.

Yes spud guns are legal in Washington, I know because a neighbor called the police on my friend and I a few years ago, but when he got there he just want us to let him shoot it