Re: Shooting Steel Safely
There's a huge body of knowledge/experience in the silhouette communities, aka "iron critter" shooting, for both RF and CF, rifle and pistol.
NRA changed its minimum distance from 25 yards or whatever to 40 in rimfire, because of the frequency of larger fragments reaching back to the line and the spectators too. That's without any target dimpling or dishing making it easier to direct bullet splash and fragments back to the line.
Range safety includes the combination of engineering and enforcement of rules which are dictated by that engineering of the range facility and its targets and impact areas. Sand is your friend, but that requires *enough* sand.
AFIC, you must always plan for more bullet to survive impact than you observe (larger chunks), at higher speeds than you observe, and straight back towards the shooter. Few "freak" events with ricochets are truly unexpected if you think things through. For example, impacts that melt lead to a gray cloud won't melt the copper jacket. See the post from mark5pt56, above.
Personally, I recommend that all steel 50 yards and closer be angled down AND either hinged at the top or just on a stand and free to fall. If they are like iron critters, their "feet" need to be behind a shield, since the horizontal top surface of those feet directs splash back to the firing line. A falling plate hinged at the bottom will sent fragments and even largely-intact bullets skyward when your speed shooters hit them a second or third time as they are falling away. Pepper poppers shot with an SMG are particularly bad for that, and I've seen hardly any ranges anywhere with an overhead cover capable of catching vertical bullets *at the target position*.