If it's commonly available today it won't be a rare collectible in your lifetime...if ever. Don't plan your retirement around all the "collectible" ammo you've got stashed in the basement. I've been a serious cartridge collector for 40+ years and have curated a rather extensive collection of rare issue and experimental military ammunition. I'll probably be able to sell the top 5-10%, and the rest will become somebody else's basement full of junk.
Sad but true.