This is how the 4th of july was often celebrated in frontier towns in days of yore...
As a blacksmith, I must admit "anvil shooting" can be entertaining..but it also can be dangerous; even moreso the larger the crowd. The overall association for North American artists & blacksmiths, will have no part in sponsoring such an event.
When you consider the things which can go wrong with black powder use..one must consider that the anvil will not necessarily go STRAIGHT up and STRAIGHT down..with a large crowd, individuals cannot always vacate a spot quickly.
There are convenient (powder holding) manufacturing cavities in the base of most anvils. However, there are times when unbeknownst to the "shooters", the anvils also have construction flaws in the base, invisible cracks...if you will. There are cases where the anvil has virtually exploded..sending chunks of steel into the crowd at black powder speed.
I hate to be a "kill-joy" ..but that's just my $ .02...
http://www.youtube.com/watch?v=q9isw0fKXAE