I had a old Browning shotgun that was my grandfathers and had a gouge that was much deeper than that. I took it to a GunSmith and had him completely refurbish the gun. I asked him how he got that gouge Out and he said with a iron. You wet it Really good and put a piece of cloth over it and then hold the iron on it and it will raise it up to where you can sand it. I’ve never tried it myself because I never needed to. That shotgun needed to be professionally done because it needed bluing and the stock done and is worth quite a bit of money. I’m sure you can Google it to get exact directions.