I am taking welding classes and we have a lot of leftover steel.  I want to make a steel target silhouette with the swinging target (and its counter weight).  Does anyone have any plans or instructions on how to do this?  Thanks

Why bother with someone else's design. Figure out one that will work and try it yourself. There's no fun in copying the work of other's, especially when it is likely patented.

simple...take a pic of your wife or ex or boss....poster size it.  Ta DA!!!  

how thick is the steel

3/8" of AR500 (500 Brinell) armor plate seems to be the standard.  Softer steel will crater/dent and welding and cutting will ruin the heat-treat around the cuts and welds.  

I'll try to describe one that I think would work.

Square steel base.
Steel tube welded to center of base sticking up (think t-ball)
Slash cut the top of the tube at about 30 degrees and weld a plate to cover the open hole.
Put a bolt or shaft through that top plate.
Make a silhouette on a shaft with a counterweight heavier than the silhouette at the other end of the shaft.
Mount to the stud at the top of the tube, done.

When you shoot the silhouette, it will swing back then the heavy counterweight will pull it back down due to the 30 degree angle its mounted at.  This would be for a semi-permanent placement as all that steel would start to get heavy.

The easy non-moving target would be to cut out a silhouette and mount it to a steel base perpendicular to the ground.

They have all sorts of steel.  They are left overs companies donate to the school.  I can get probabaly 1/2 steel, but I am not sure how to tell if its just mild steel or the hardened steel I need.  I probabaly need to arc weld this.  I was thinking about building a steel fame similar to a swing set.  The legs would be pipes with smaller pipes as detachable legs (to transport).  Also the top rail along the top of the swing set would be pipe.  I will slide a larger diameter size pipe over this to act as a hinge. Then I guess I'll weld a target and a counterweight on top.

I made one up in welding class that was just a 3/8" thick 10" diameter plate and made up some hangers to attach to it.  I hung that from a piece of $1.50 rebar I got at one of the hardware stores.  At the time we were shooting in a gravel/sand pit, so I just pounded the frame into the ground.  It worked great with handgun rounds, but the .44mag moved it quite a bit.

Wish I still had access to the welding shop.  Good luck with this and try to give us a couple of pictures when you get it done.

If it's "scrap" that's donated, it's probably not hardened, at least not to the 400-500 Brinell.  Lesser heat treated steel is pretty common though, so it may be harder than "mild steel".  A machine shop could test it for hardness, but that's probably outside the scope of a shop that just does welding.  

One of my in-laws works for a welding shop and made up a target for my father-in-law.  IIRC the legs were flat triangles on each end, then a pipe/rod for the cross post.  Cross post was probably 15-20" off the ground.  The targets themselves were three double-ended paddles.  Hinge was a pipe around the post.  Rods to the target paddles, flat circles for impact plates.   The plates were circles, with the top one a little bigger than the bottom one.  IIRC the first was 1" & 2", the second 3" & 4", and the last one I think 6" & 8".   By having both a top and bottom they were somewhat balanced and would spin nicely when hit.  By having the bottom one bigger than the top one they always came to rest facing you.  Worked nicely, but didn't hold up very well.  We were shooting .22s at it from 25yds and by the end of the day the plates were bending and welds cracking.