It's not just steel core. Much of the Tula, Herter's, and RWS ammunition on the market has a lead bullet with a steel jacket and copper coating. It's often referred to as "bi-metal."Most ranges I know don't allow steel core ammo simply because it really batters the impact plates in addition to the spark issues.
That stuff actually generates worse sparks from what I've seen. The problem for buyers is that it doesn't say that anywhere on the box, and many of the shops selling it don't mention it.
So, customers buy it because it's the only ammo around at a reasonable price. They take it to a range, and they're told they can't shoot it. It's not a fun conversation.
As Doc Intrepid mentioned, a magnet is the best test.