I watched the BDS webinar doodaddy with Andrew Venables who mentioned ricochet, he said that the audible ricochets aren't the ones you have to worry about as they no longer have gyroscopic stability and their energy and flight path is relatively short. I'm sure he said that once the sound has finished they have come to rest. Or I may have imagined that bit.
I'm soooo paranoid about ricochet and pass up quite a lot of shots that I think about after and would moat likely have been safe but I'd rather it be that way around than the other. Especially given my topography here, and when the weather is dry the ground is like a rock. and when it's wet it's full of bloody great big flints.
I don't shoot any differently regarding backstop with lead or non lead but I can understand how having a bigger lump of metal flying out of the back of the deer might be more worrying to some people. For me. With regards to backstop I always work on the basis that I am going to miss so I guess you imagine that the bullet, on striking the dirt has the same weight made of lead or copper, and you can't guarantee that even varminting fagmenty bullets will break up.
I was terrible at maths and physics at school so a lot of ballistics stuff goes over my head but it would be useful for someone to fully address the difference in ricochet between lead and non lead ammo, demonstrating how ricochet works and what it means for a monolithic bullet versus other types of bullet design.