Been using a 16 inch pine log for a .22 backstop and 100 grain plinkers for about one year now. The center is about shot out and I'm nailing two pieces of 2x6 over the center. Even some of my plinkers are going all the way through the backstop now and some of my "hotter" .380 ACP loads are blowing all the way through to the second 2x6. It's about time to split the log up into kindling and see what drops out. Bet there is a good 10 lbs of lead in it.
Had a couple ricochets when shooting a black powder .50 caliber round ball with a light load into the log. The ball would dent a hole into the pine and then bounce straight back at me. Put a some nice dents in the side of the shop before I got wise. Had the same thing happen with a B B gun when I was a kid and got hit in the leg.