I'm not sure that the wife could legally hand the rifle over to the ex-husband if he showed up on the front porch.
Having title to property is one thing. Having possession is another. Interstate transfer of title is, as far as I know, not regulated. Interstate transfer of possession is regulated, and both the giving and receiving party commit felonies if an interstate transfer is done without an FFL.
Title to the property is probably held by the wife, if the standard 30 day possession clause is in the divorce decree. Like so many things in a divorce, he may have bought it, and it may have been his at one time, but it probably is now hers. And the wife clearly has possession of the property.
Even if the ex-husband holds title to the rifle, she probably commits a felony if he shows up at the house and she hands the rifle to him. The ex-husband lives in NY, he's not a resident of your state, and you can't transfer possession without an FFL.
Be done with this negative interaction. You don't need more conflict in your life. Either tell him to pound sand, or tell him you'll turn it over to an FFL in your state and he can deal with it from there. This is simply not worth the emotional investment it's getting.
OP lives in Colorado. The transfer would require a background check through an FFL.
You didn't use logic or reason to get into this opinion, I cannot use logic or reason to get you out of it.
You cannot over estimate the unimportance of nearly everything. John Maxwell
