These targets do not stop most bullets, you will still need a backstop to catch your bullets.These targets are not invincible, and will periodically need to be replaced or repaired, but since they're made from recycled materials it should be cheap or free to fix.
This is the part where I warn you to be careful and always observe proper safety procedures. No one likes getting shot(at least not anyone I know) and hospital bills/jail time can really ruin your day. Be careful because if you get hurt, it's not my fault, and depending on how serious the injury is, I may laugh at you.
Step 1: Supplies
7x Wire frame storage shelf panels
Lots of light gauge steel wire(probably over ten feet, it was holding a roll of chicken wire together) This could be replaced with zip ties though assuming you used some decent zip ties.
2+x cuts of gardening tie(mine are just over a foot long, and not the same size)
3x Brass hooks per cut of gardening tie(again, feel free to make substitutions)
1X Roll of duct tape!(if you have lots of wood around you could skip this, but I'd do it anyway)
I didn't include a list of tools because each build is a little different. You know what tools you need.
Step 2: Building Your Frame
If you look at the picture you'll notice that I have a simple rectangular shape for the perimeter. I overlapped the the top and bottom sections by about a third of the panel so they would stay linked as one panel. If you link them end to end, you will end up with a very floppy rectangle.
Also notice that in the bottom section, I tied one panel in at an angle. I could have tied in this panel perpendicular to the other panels, but I was worried that I might damage my frame while shooting. By mounting it at an angle, I left more of the back open, while still giving my frame a decent support system. The angle is NOT there to catch bullets. It's a wire frame, it would be useless for that.
I would suggest starting with the outer box. I didn't, and I had some very minor issues with holding panels in place while trying to tie them together.
Step 3: Build Your Danglies
Cut your wood into pieces about 1 foot long. When you pick your piece of wood for this, you might want to consider a few things:
Can I hit a target that size?
Will my projectile destroy a target that size?
How often do I want to replace this?
Can my frame support a target that size?
I cut my pieces to about a foot long because that's what fit inside my frame, but now that I've done this once I might have built a heavier frame for supporting super heavy targets for a wider range of weaponry. I don't have anything heavy enough to really cause a problem with these targets, but a few of my friends do, and they like to shoot at my place. I'm rambling again...
Next is to screw three brass hooks into one end of each danglie. I put two in with the open end face the back of the target, and one facing the front(in between the other two) to keep my danglie from being knocked off of my frame. These hooks will allow your danglies to dangle and swing when you hit your target.
Notice the duct tape in the picture. I added this after my first target practice because I actually broke one of my danglies in half. The duct tape will help hold your danglies together for quite a while longer than if you didn't have it. You could also wrap the entire danglie in duct tape for super long life. Colored duct tape would allow for different color targets making it easier to call your target when shooting with friends.
Step 4: Put It All Together
Hang the danglies so they're centered from front to back. If you have them too close to the front or the back, they're likely to tip the frame over when you shoot them. I suggest that you keep an even amount of space around all sides if possible. These thing really swing when you hit them and you don't want them smashing up your nice frame, or each other. You don't need to stake it down, but it wouldn't hurt. Make sure you have a good back stop behind your target or your bullets could go places you don't want them to.
If you're shooting at your danglies but missing it can be difficult to tell where you're actually hitting. Try removing your danglies and using a few clothespins to hold a paper target on your frame so you can see where you're hitting.
If you know you're hitting your danglies but they're not swinging, try shooting them closer to the bottom, or try cutting the danglies to a short length.
Feel free to make modifications and share your own setup. It took me about an hour from the time I had the idea to the time I took my first shot. It shouldn't take you that long. When I get a chance I'll post a few more pics and a video of the target in action.