I used to manufacture metallic silhouette targets.
There are many good steels for this purpose. I used T1A but that can be hard to find and is no better than some others.
The key is to allow the targets to swing freely. And, if possible, have the angle downward as they hang.
If you put on bases make sure the bases are only large and heavy enough to hold the target upright. Too much of a base can result in fragment splash back.
As said, 10 yards is too close to be shooting steel.
My jury is still out on soft/slow bullets vs. hard/fast. I am inclined towards about equal from a safety standpoint. They do react differently but the bottom line is about the same.