I concur with the above; I had an article published on this subject not so long ago.
Guns make poor investments. They do not earn rent, dividends, interest etc, they require maintenance, storage, insurance etc.
They rust, break, go mouldy, wear out...
The only way to make money in guns is with arbitrage - knowing a bargain when you see it which could conceivably be turned over quickly at a significant profit. You really need to know your field, hunt hard, and be lucky to spot those bargains.
Buy 'em 'cos you love 'em, not 'cos you'll make your fortune, 'cos you won't!
RG