Steel shot damage?
 

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?

kinda looks like rifleing...wgo knows what went down that barrel....charlie

Not Steel Shot
 

I know this is an old posting, but I wanted to put two cents in. I'm not a fan of steel shot and like most of us waterfowlers I think outlawing lead was a typical half-baked liberal idea that still makes zero sense. But, that being said I've been loading steel shot for a good 4 decades and I always try to collect my empties and fired wads if I can in the field. One thing I've learned over the years is that steel shot loading requires a special hard plastic shot cup wads that the shot sets in and shouldn't extend above the edge of the wad. When fired that wad carries the shot out of the barrel and generally a good 5 or 10 yards further before falling away as the shot disperses. In all these years of shooting and loading steel shot I have yet to find a expended wad that showed any sign of the steel shot penetrating the sides of the wad. Which clearly means that if loaded correctly steel shot loads should never damage a barrel by scoring it as it travels out of the barrel. That heavy steel shot wad is all that ever touches the barrel. I even have a friend that occasionally uses his Briley 20 gauge sub-gauge tubes during early duck season and he has no problems with steel shot damaging his tubes and they are made from aluminum. The evidence I've seen firsthand over the years tells me that a lot of the steel shot damage to gun barrel stories are just that, stories, without foundation or evidence. Now I would not suggest a heavy load of steel shot be fired out of a full choked barrel, because that is another matter altogether. Steel shot won't give like lead or even bismuth, so any constriction tighter than modified can risk damage to the choke.

I loaded a LOT of steel back in the day. You are correct, special hard wads (we had to split'em by hand with a tool) and no shot above the cup. I'm not sure what went down this set of barrels but it wasn't lead or bismuth!