Ventilation (lead, mercury) should be as big a concern to you as stopping without ricochet.
I would look towards softer backstops instead of rigid ones.
A milk crate or similar size box stuff with crumbled rags/clothing stops a 10mm auto every time without fragmenting bullets.
That would work but one problem I have found with rags and phone books is that if you fire a couple of rounds in the same spot then eventually they will get through.
I have seen the use of heavy steel sheets mounted at 45 Degree angle over a box of sand. Depending on the steel used and thickness depends on the success of containment. My gunsmith used such a system in his shop. The rumor is that one of his customers had picked up a "458" rifle (Winchester or Weatherby??) and they test fired it into the box. The bullet was contained but had almost destroyed the steel plates. It looked like some one had taken a sledge hammer and hit a thin sheet of tin. The plate was really bowed out where the bullet hit. Barry told me that when fired he immediately knew he had made a bad mistake. His shop was in the basement of some old buildings in West Columbia, SC. Dust fell from the ceiling and every body has to vacate the shop until the dust settled. He also mentioned that the noise was very loud and that the hearing protection that he had was not as effective as he had hoped.
The bottom line is that you can build a containment system in your home that will work but be picky with what you fire into it.