it looks like some of the AA-BA problems with transiting firearms through London MAY have been resolved...
I just spoke with a customer service supervisor that read the current American Airlines policy to me... in a nutshell she advised that the general policy for AA allowing firearms for international travel is that when a firearm is checked onto the aircraft the traveler must provide a copy of the entry permit for the country of destination...
and.. specific to transiting London Heathrow she advised the policy states "due to local handling procedures at LHR, a service charge of $80 will be collected at check in"..
planning on doing a little more research.. and would like to get my hands on a copy of the policy as well as a senior manager at American to confirm/deny what I have been told...