The old Winchesters in calibers that you can't find are still worth good money. I would say it depends on the gun, if it is a collectible piece cartridge won't matter as much. If it is just an old gun for utility use, then it needs to be an easily available load to have much value.

My Opinion Only-if it's a gun you are not going to use, then look at it as an investment, using the same kind of criteria.

I have a couple like that, I thought about selling them but can't quite bring myself to do it just yet.