So I was shooting quail in South Georgia this weekend and, after taking a shot at a bird, the guide said it sounded like the gun doubled. I knew it hadn't and wasn't too concerned until I looked down the right barrel and found a piece of the wad firmly wedged in there (pic below). We had to basically ram it out from the muzzle end. The plastic was so hard and it was so tight it seemed like it would have been impossible for that to go through even a lightly choked gun.

I was super paranoid about it for the rest of the hunt and checked to see if the barrels were clear after every shot.

What causes that? Is that a defect in the shell? I feel like I narrowly averted a blown barrel by chance and that makes me extremely uncomfortable.