I've been shooting armor steel targets in long-range matches since about '03.
The best method we have found - bar none - is to use one piece of conveyor-belt strap approx 4-5" wide to hang the target from an A-frame stand.
On the target end, there is one hold cut through the armor steel, with at least 1" of metal between the hole and the edge of the plate. Put a grade 8 bolt through the hole, then through a hole cut in the strap. On the back, use a large washer and then a nylock nut (does not have to be grade 8). Do not tighten the nut down all the way - the plate should barely be able to swing side to side freely.
On the other end, cut two holes in the strap and fold it over itself and bolt through to make a loop. The cross-member of the A-frame stand goes through this loop.
The A-frame stand can be made of rebar or it can be something more involved with bar or tube stock and welded "corners".
These targets are extremely durable and will only fail after multiple hits to the bolt head itself or multiple hits in the exact same spot on the legs/cross of the A-frame.
The conveyor belt material can absorb many many hits and practically unlimited splash and not fail.