Wonko
For your information seam in modern steel happens when a bit of "dirt" is poured into a cast steel bar, often continous cast and then rolled from the hot band to the finished product. A .10 round bead of material is flattened and lengthen as the steel is rolled and can result in a seam of "dirt" that is only.0003 thick and two feet long. This then ruptures when force is applied to it (a shot) I have seen this on connecting rods and on .026 stainless. You can't see it on the outside but it fails real quick. I believe the 870&1100 recalls were due to Mn stringers, seams.

Bill