Sparkz,
About 15 years ago, I tried stacking up some railroad ties & using them for a backstop. Everything was find until a shot hit right at the seam where 2 of the ties met. A lowly .22lr went right out the back.
If you shoot at stacked wood, you need to have something behind the seams. If you cut thick cookies out of a big log & shoot into the flat end, you are probably safer. I think that if you look back about a hundred pages or so, you will find pictures that were posted by people who shot into stumps & then burned them to recover the lead. As I recall, it worked out well. I suspect that the act of burning the log acts to flux the lead as a bonus.