This is a CVA Optima V2, I imagine that it was shot with a saboted bullet. Of course, it could have been shot with one of the Powerbelt types or even a lead conical. I have cleaned the rest of the gun and fired it myself with sabots. I have some old sabots with bullets that may have left the residue--I did not notice it until after I had shot it a half dozen times. At any rate, it is accurate so I want to clean the barrel up good and keep it.