Some of those guns are assembled by Italian Gorillas, and yes, they can be difficult to remove.
You're on the right track using the wood, but you might need to go to something like a piece of brass. Support the off-side of the gun as well as you can with padding of some sort, and and give it a good swat. I'm not saying to be careless about it, there are ways to use a good amount of force, and not harm things.