I agree with EC121. Lowering the wood to half the width of the side flat and reshaping the panel will nearly take care of the issue. I did a similar repair as well. I did use some Acura glass to fill the cavity and let it cure before I reshaped the wood in that area. In my case, I was able to use the black stain and brown stain in the Acura glass kit to get the color very close to the color of the wood in that area. The texture was slightly different than the natural wood, but I was happy with the repair. I was lucky in my instance because the flaw got much smaller as I worked the wood down. I showed the customer the before and after and he was happy with the finished rifle. It has been in use for several years now with no issues. Using fancy wood leaves us open to running into flaws that are not visible until we work the stock down. I scrap a $400 piece of sugar maple about 15 years ago because of a bad spot in the wrist that did not show up until I worked the blank down to nearly the finished profile. Bummer, but it was one of those times that I lost the battle.
Roger Sells