Here's our original system--
The legs simply slide into the "swing set top" i put together by using some of that liquid weld or whatever it's called, to glue all the angle piping and horizontal top pipe together. It should be easy to figure out if u look at it close. This is a pretty portable system that works very well for the heaviest of targets.
Here's what we used for our SHOTS (Specialty Handgun Outdoorsman's Tactical Seminar) shoot we put on this last May, that works terrific for portable smaller tgts, even heavies would work too. Set up 30 of these in 1 day, and took it all down in <3 hrs. Best to use galvanized pipe T's for the tops of the vertical rebar (copper works OK too), as the plastic get shot up fast. If u ever get to Pueblo, CO (I25) let me know i'll take u to Spekens Metal Yard, and u can get some of these tgts. cheap. U can't touch it with a bullet or carbide drill bit-- they're heat treated cinder block molds, and they last forever.