3/4" steel is a terrible choice for a backstop. You need a berm.I have a 3/4" steel backstop at my range. The reason being is that 223 would penetrate.the 1/4 steel that stopped the handgun rounds would not stop the 223 and other HV rifle rounds. I have 3 miles of wood behind my house. And still it is important to know where your rounds are going ( at least it is to me). Safety first!.
I will mock up a wall this week and shoot it with 223, 556, and 9mm and let you know what I find in the recovered bullets. I will use the 9mm 124hp and the horn vmax 223. And green box 556.