I've never really looked at mine as investments, although I suppose they are worth a little money. The rare firearms will always be worth some money, and if you're a collector of say, 1873 Winchesters, then your rifles will always have value to them. On the flip side, if you bought some AR's years back when they were fetching a premium, and you want to sell them now, you're going to lose money.
As an example, my late brother had a nice gun collection, and when he knew he was dying from cancer, he told his wife that it was his wish to use the guns to help send his grandkids to college. My ex-sister-in-law contacted me recently about helping her sell some of them, and I agreed to do so. She had gotten a neighbor, an "internet expert" to look up some prices on some of them, and of course the fool went on Gunbroker and looked up some of the prices on guns that someone is hoping to sell for more than it's worth. When I told her that her $1200-1500 rifle is only worth $500 today, she must have thought I was lowballing her, because I haven't heard back from her.
The thing that a lot of people don't get is that while some guns hold their value, and even increase, others do not, and with this being a buyers market today, many sellers are disappointed when they try to unload theirs.
