Dan:  This Federal firearms law that they are being prosecuted under ( section Section 924(c) of the US code ) was originally created by the Congress for mainly dealing with violent drug traffickers.   That is why it is so severe.   It was not created for people engaged in dangerous armed political protest.   There really are no laws that have been created to cover these kinds of acts, so the government has to use what is available under the law to prosecute.   

Here is a link to a chart showing the sentencing guidelines for this law:

http://famm.org/wp-content/uploads/2013/08/Chart-924c-gun-MMs-NW.pdf

It is much like how the Hammond family was prosecuted under the Federal Anti terrorism Effective Death Penalty Act of 1996.   The crime created in that law that they were prosecuted under was originally created by the Congress mainly for punishing terrorists who destroyed Federal property.
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