Obviously, you can't offer more than the gun's value in buyback. But you have to offer enough for it to be an incentive. It's certainly a dilemma, and that's why gun buybacks probably can't work on their own. They must be part of a broader strategy that offers additional incentives. Offering tax breaks for guns, in my opinion, gets around this somewhat by divorcing the incentive from the value of the gun. It's a good idea, but I think it requires some work before it's effective and useful.
Actually, in the past several programs doing buyback did, indeed, buy any gun turned in. A lot of very dead guns got their owners some nice fundage. That does not trouble me (absent it being my tax money used for the buy-backs) as I strongly suspect most of them were done simply for political expediency so the group sponsoring same could look like they were helpful pillars of the community.
.223 fired up in the air has a range of around 2 miles. Unless its a rabbit thrower on the ground, I suppose that's OK.