[RWebb]

you might be able to offer to disable it and keep it

or

1. tell BATF you WILL donate it to them for their museum, but you want the value stated in writing so you can take it off your taxes

2. tell them you want compensation for the "takings"*

dunno if those will work or not, legally

* normally, applies to real property but maybe it applies to, or can be made to apply, to chattels