Well, I may respectfully differ with a few folks.
Take the Steyr AUG example. Using swampgator's numbers, this works out to a little more than a 12% return, compounded annually. The accepted 'normal' equity (stock market) return is a bit over 10% - lots more in the last decade. And, that is one firearm, and a fairly exceptional one I believe.
Like many classic cars, often such investments only look good if you don't compare them to the alternatives.
I'm sure we could find unusual and more collectible pieces that have a higher rate of return ... but, I think those are the clear exception. And, the part in the Blue Book that troubled me (and, I'll bet Paul as well), was the writer's advice to buy 'unusual' calibers. I feel the same as Paul ... I want firearms that have readily available and relatively cheap ammo. 9mm, .38 Spl, .357 mag, .223, .308, etc. I just feel that any firearm I own should be capable of being pressed into defensive duty.
But, another way to view this may be from a standpoint of investment diversity. Firearms provide some inflation hedge, are generally prized commodities, serve a potentially life saving purpose, represent an educational opportunity for kids [that will drive the anti's crazy
], and can be used to gather food.
So, I see firearms as rather a cross between a commodity investment and an insurance policy. The highly collectible ones are more like numismatic / rare coins. Tell your friends that your guns 'serve a unique niche in my investment portfolio'. That'll get 'em.
Regards from AZ