I don't mean to "poop" on your PVC project, but the horizonal "base" pipes probably need to be longer OR anchored into the ground. The way it sits right now, a sudden gust of wind might blow it over, and it will probably "dance" somewhat when rounds strike the target.
You can anchor the base pipes fairly easy, with holes drilled through the PVC and using some long spike nails hammered into the ground.
Instead of using the horizontal pipes for the base, you could also pound some long spike nails into the ground, with enough of the spike lenth above the ground so that you'd be able to slip the vertical pipes over them.
PVC projects are FUN! I built a PVC sun shade that goes out with me every time. It's just big enough for one shooter, but could be engineered to have more room. The "sun shade" part, that fits on top of the PVC pipe, is nothing more than a large piece of cardboard! I think that I invested a total of about $6 for all the PVC stuff.