Steel shot damage?

[Keith Doty]

Pics of another Damascus gun I recently looked at. The continuous vertical ridge is the end of the chamber. The scallops in it and the grooves going toward the muzzle look like something very hard had been down this barrel. When you stuck a finger in the muzzle and rotated you could feel the grooves. They ran the length of the barrel. Gotta be steel shot or BBs. As this was a 2 7/8 chamber 10 ga., I'm trying to figure out where the ammunition came from. As far as I know, all the 10 ga. ammo produced after the steel shot was forced on us for waterfowling was 3 1/2". This damage is too far back to have come from that long a shell and I don't think you could possibly stuff a 3 1/2" in this gun. Handloader with steel BBs?