I'm considering making my own steel silhouette torso target - my rough sketch is below.  I'm not sure how thick the steel should be or whether to use mild steel or something harder.

 

Hard steel is brittle while mild steel is more ductile.  Dents are okay as long as they don't become punctures.  Harder steel is stronger and won't punch through as easily but will fatigue fail sooner with repeated shots and might crack just from being brittle. 

 

I also want it thick enough to handle what I'm shooting (.308, 9mm, .40, .45, .223, and it would be great it it could take 12ga slugs) but light enough to swing satisfyingly when I get a hit.

 

My initial thoughts are mild steel 3/8" thick but at almost 40lbs, I doubt I'll get much of a satisfying swing when I hit it.

 

Any thoughts or advice from those more experienced with shooting at metal?

 

stay away from mild steel. AR500 is what you wat. The dents and craters cause unpredictable ricochets.

Check here:

 

http://njgunforums.com/forum/index.php/classifieds/item/412-ar500-12-thick-steel-targets/

 

Already made up AR500 1/2" steel silhouette cut by a water jet. I guarantee it is cheaper than you will be able to build it yourself.

 

I bought 2 last year. I have shot all service handgun rounds, .223/5.56, 7.62x39, .308/7.62x51, .30-06, 8mm, 12 00B and Slug all on it with no issues. I regularly shoot 5.56 inside of 10 yards with no splash back and very little dimpling.

 

Avoid green tip and .30-06 armor piercing, that will pit it. I had a student that was loaded with green tip and I didn't know it. After a string from the 50 yard line it was dimpled pretty good.

 

Also, like Henry said - dents/dimples in steel targets are bad. You can not predict the angle the slagged round will rebound at if it hits a dimple or dent. You want it to stay as smooth as possible so you don't get hit with ricochet or frag.

I made some out of 3/8 mild steel. At about 80 yards my ak went right threw it and my mosin well lets just say it DESTROYED it.