While real world data is good, it tends to be a bit anecdotal -"it worked great bang flop" versus "penciled right through and away he ran" Both happen. The problem with this sort of question is that it would need thousands of shots to be compared from lead and copper bullets in roughly similar situations with flight distances accurately measured. What we can go on is the data from ballistic gel where it seems that copper penetrates more and makes smaller temporary and permanent wound channels. Copper releases energy slower than most lead bullets. How much measurable real world impact does this have is beyond the an individual's ability to answer in a way that clearly proves something to those who disagree.
What would be great would be if somone with no dog in the fight did proper research, not a bullet maker or a government funded body. BASC could have taken the lead on this instead of just jumping to toe the line. They could have got several hundred regular stalkers to use only lead one year and only copper the next and record every hit, every lost deer and measure every flight distance, then looked at the macro data. They could have also looked at the data for prefragmented tin, then chosen whether or not to advocate going lead free. Instead BASC has toed the line, not led the way. This is not what we need from a body that represents us, they are making an accomodation to avoid rustling feathers with politicians before they know if it is a good idea.
We are arguing about what are our hunches and our experience says when it comes to lead free and this is the problem. If we had hard data, we could relax because the truth would be in front of us and we could move on with confidence.
The bullet manufacturers, and those shooting lots of deer have all done their own research. Fundamentally non toxic bullets have been around for many years now, have been the go to choice for many in many different countries because they perform better on big game animals.
The biggest challenge with cup and core lead bullets is to rapid expansion and failure to penetrate, hence development of monolithics that penetrate well.
Now we have a good variety of bullets to choose from. Some like the original Barnes or the Hornady GMX are tough bullets - probably too tough for most UK / European deer.
Others such as the RWS HIT or the Fox are designed to expand at normal rifle impact velocities in European deer species. They work well.
And if you want rapid expansion, lots of blood loss, then there are fragmenting partition type bullets. RWS Evo Green, the Brenneke and I think Sellier & Bellot are using.
Go back three or four years there were endless discussions about failure of different types of lead bullets.
And there is not yet in the UK a legal ban on lead ammunition. So you can carry on using lead. But game dealers have chosen to only accept venison shot with non toxic bullets from the middle of 2022. That is their choice about their own business.
As for steel shot in shotguns. It works in the vast majority of guns and shooting situations. Some may have to adapt - use a different choke, or have chokes opened up, and velocities are a little different so you might have to adapt your swing - but to be honest I have found a difference between different brands of cartridges - some just seem to work better fir me than others.
