I'm not quite sure what you mean. The "base pin" is what the cylinder revolves around. It's #21 in this diagram. It's fixed to the frame, and to avoid damaging it or the frame, it should only be removed by a gunsmith. The barrel is held onto the base pin with that wedge. If you've gotten the wedge out, but are having trouble removing the barrel then there's one quick way to work it free. Rotate the cylinder so that there is not a chamber lined up with the rammer, and use the loading lever to force the barrel assembly off of the frame.
Edit: If there's some rust sticking it together, you could always try some penetrating oil. Even good old WD-40 might work. Just let it soak in overnight, then try to pull the two assemlies apart.