You could consider having all the metal plates bent vertically so that they are presented more as a wedge. That would have the BB's deflect to the side on impact (vs. back at you where they'll go everywhere).
Not great though if there's other angled plates that will redirect ricochettes back at you...that happens at TTAC all the time. The boards are setup at an angle behind a target but the shots will reflect off of another surface and come back.
You could also hang the metal plates vs. having them hinged. 99% of the shots would be deflected offline in some direction...still lots of force left for rebounds though. Much slower return to ready as well...they'll just spin forever.