In my experience, maple heartwood is often not suitable for a gunstock. Sometimes it can be hard, abrasive and prone to cracks at the heart / sapwood interface. I have had some cases where the heartwood was more tolerable in that it was a lighter shade, not so hard, abrasive etc. Guess it just depends. In the cases where heartwood is tolerable, ferric nitrate stain seems to even things out well. I must say that when I've used stocks with a heartwood, it has been a small amout, usually at the tang area or toe. Not a large percentage of the stock.