That's his problem. They should have been kept in a well oiled flower bed.
Mr Fincher's purpose was to challenge the the govm'ts violations of the 2nd Amend directly in a decisive way. Note that he is not a criminal, was not engaged in criminal enterprise and produced the guns with the sole purpose of mounting a challenge to the laws.
LOL That might have been a good idea. It appears that he wanted to make a federal case out of it though. For those who simply want to be prepared and don't want to see how far they can get standing on the intended protections of the U.S. Constitution the following link may be of use.