Getting paint off a gun

So my sons GF dad asked him if he wanted a shotgun. He said it was a belgian browning automatic, my son says Hellz yeah. Apparently the gun came from an old man that before he died painted it, the whole thinmg camo greenish and brown. The paint on the barrel is thick as hell and I soaked some paint thinner on a couple paper towels and let it sit for 15 min but it didnt budge. Whats best to use on barrel and reciever? What about the wood?