I ask because I have two Laurona 3in Magnum 12- bores and wonder if they are suitable for steel? Should I check with a gunsmith?

Yes, there is a difference. Without seeing the guns I can’t tell exactly, but I believe your Lauronas would be proofed to 1,200 bars, which would mean they are safe with 3-inch magnum lead cartridges.

Steel shot proof is something different, and the mark includes a fleur de lis, which is a symbol similar to the Boy Scout badge.

On multi choke guns the choke tubes should also be stamped as being suitable for steel shot.

In short, it is neither wise nor safe to shoot 3in steel magnums through a gun/ choke combination which is not proofed for such a load.