Well, berms are not such a good option either. Here in Germany we don't use them anymore. The army here also had a outdoor range with berms, for the pistol and submachine gun training, but it had to beclosed many years ago because the lead poluted the ground too much. A berm makes it difficult to collect the lead and dispose it properly.
The best bullet stop I have seen was in the local police shooting club range. Since they were shooting all calibers, they had installed a very solid rear wall. It was a large vertical steel plate, of 1/2 inch or so, and then horizontal steel strips welded on it in a 45° angle pointing downwards. The strips were about 5 inch wide and welded on in a way, that a bullet would alway impact on a strip, not directly on the rear plate. This way the bullets always get deflected upwards from a strip and then get caught under the next strip above. Kind of difficult to explain, sorry...
This way the lead drops down to the ground in front of the bullet catcher and can be picked up easily. Also it makes less ricochets than a flat wall and lasts longer.

Btw, do you know that indoor ranges have to get cleaned frequently for safety reasons?
Its because with every shot a tiny bit of unburned powder gets spewed out. Over time, it can collect in corners and on the walls ect. - and then suddenly ignite from a spark!
Many years ago there was a accident like that in a indoor range in Germany, that killed some people.