A cross section of a tree shows the growth rings. Each growth ring while of the same tree produces wood of a different density based on the time of year, nutrients, water, etc that the tree has access too. More dense wood accepts stain less. more porus wood accepts stain more easily.
Most stocks are cut following the grain of the wood because this makes them stronger. knots or cross grain cuts are generally avoided as they can cause weakness, especially knots. Your stock has a lot of cross grain showing in the forend. Doesn't mean it is weak, many civilian arms have those cuts simply because of the look. Not all that common with military arms.