So, instead of a "buy back" we should call it forced confiscation with token compensation.
I'm guessing they don't really care if you turn your gun in or not. They kinda win either way. If it's illegal to possess and you don't give it up, what do you do with it? You can keep the "illegal" gun hidden away for SHTF and in most states, no one will be the wiser. Or you can take it into the BFE desert or wherever to shoot where no one else is around.
Most law abiding folk won't take it to the range though, for fear of somebody dropping a dime on them. If you have a job and a paycheck and health insurance, you're gonna worry about what an arrest and criminal conviction will do to your life. Criminals have no such concerns, and I don't think these people give a *expletive deleted*ck about the criminals - they'll happily call disarming us, or making us hide our stuff in an attic, a win.