I've only sold one gun that I've ever owned. It was a Ruger P89. Shot a box of ammo through it and didn't like it. (Double stacked magazine felt like a shoebox in my hand and it shot low and right.) The 1911A1 is much more comfortable for me.
Sold the P89 at the next available gun show for what I paid for it before the AmEx bill showed up.
Every other firearm I own is worth more than I paid for it.
I don't know about "investing" in firearms, but my experience is that what you pay today is less than you will have to pay in the future.
And if you need to liquidate "hard assets", IMHO, firearms will be easier to recoup your original investment, with a possible profit, than jet skis, boats or autos.
I don't consider them investments, but assets which do seem to increase in price over time. Of course, whether their increased value matches or exceeds inflation is not part of my equation.
FWIW
GB7