My hammer's only 6lbs, but anyway, it's well worth the investment to get a lead hammer. WAY easier than say a small sledge and a 2x4. This is what you want:
http://www.americanhammer.com/
Here's a video of how to do it:
http://www.youtube.com/watch?v=X8kCWG3d1Cc
And make sure you safety wire it when you are done.
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