I would like to see a ruling from the ATF or even a law that says you can't "invest" in firearms. I absolutely think you can make a long-term investment in firearms. People do it all the time when they buy a nice rifle and keep it in pristine condition. That's what collectors are doing. And even if they don't ever sell them, they expect to pass along these valuables to their children.
Investment is not the same as being in the business of selling firearms. If you buy a lot of firearms, keep them for short periods of time and make money selling them to other people, then you're in the business of dealing firearms.
But if you buy a high dollar firearm, keep it for a while (years, decades, whatever) and then sell it because someone offers you money you can't turn down, or you are forced to sell it to pay for medical bills or rent, then you're not suddenly a firearms dealer.
I would argue that it doesn't matter what your intent is when you sell the firearm. It matters what your intent is when you BUY the firearm. So if you buy a gun (or guns) because you intend to resell it (or them), then you're a firearms dealer and need a license. But if you buy a gun because you think it will appreciate in value down the road, then you're just a collector/investor and you don't need a license. And if you never intended to sell it, but are forced because you can't afford rent, then it doesn't matter why you're selling it. If I have to sell my car to pay rent, I'm not suddenly a car dealer, am I?
Obviously the ATF takes weird positions on things. I'd like to see some documentation from the ATF that selling firearms that were "investments" or because you need the rent money somehow makes you a firearms dealer.
There is a separate issue that you have to take into account when dealing with NFA items. And that's the trust route for approval. If you form a trust with beneficiaries, then any property in that trust is generally supposed to be held for the benefit of those beneficiaries. You've got to be careful when creating the trust to allow the trustees to use the item. Using a firearm usually reduces its value, so you'd be acting to the detriment of the beneficiaries by depreciating the value of the trust property. There's ways around that when forming a trust.
What is interesting is that a trust applying for a tax stamp IS investing in firearms. That's the purpose of a trust. So I would think if you go the trust route, that'd be the most honest, legally-true answer. But it's different than other firearms purchases, because it isn't an investment for the trustee, who keeps and uses the item, but for the beneficiary, who has to be a different person.
Aaron