Firearms need to be cleaned every year, at least. If you stored them clean, but did not apply oil and lubricant, depending on where you live and how it was stored, time will take its toll eventually. If you did apply oil and lubricant, in a year it will dry somewhat and slowly not protect it anymore. Its still something, and in ten years it will keep itself fairly well-maintained, depending on other circunstances.

The once-a-year rule is golden because if you skip an entire year, it will -still- be enough that it keeps itself perfect. Gun warehouses have that rule so at least every two years, stored guns are kept crisp clean.

Clean firearms with the normal stuff you use. Oil it, heavily. (Use a ton.) Axel grease, coat the whole firearm, any metal parts. Forget the inside of the barrel, just be sure to cap it with a condom. (Not a used one, smartass. No lube.) Grease the inside of the chamber. Really gum it completely shut at the bolt/breech. Close the action with the grease in place. Wrap in plastic bag. Get as much of the air out of the bag as possible. Lower, say a pistol, into a bucket full of water to displace the air and seal it. If water gets into the bag, you're starting over. Bury inside a water proof container. An unused, cleaned out and dry (this is key, dry) cooler will work. Anything that won't leak. This can be buried, but people have metal detectors. (Look up how deep you want to go for yourself. Geography and metal detector evasion, ect.)

To clean, use diesel or kerosene. Zippo lighter fluid would work, but you're going to need several bottles. Have towels you don't care about handy. Use gloves.

Good luck with your... Uh, friend.

Dust can accumulate, oil/lubricants and migrate away from where they were applied and/or evaporate. Best to pull them out every so often and give them a wipe down at the very least.

• asking for a friend
• wants to know if gun that has been sitting around for awhile will still work, but words it as a maintenance problem
• clearly does not use or think of gun often, but today it is on your mind

Did someone forget Valentine's Day?

Long term storage: drown it in gear oil in a sealable Mylar bag. Have to clean completely before use, but you can literally bury it and forget about it for 20 years and it will be fine- if you put the Mylar bag in a drum or something that is.

I have had a few firearms that only come out a few times a decade. They get lubed before use and after they get cleaned and oiled and greased to manufactures directions (or as close as possible with the 100 year old ones, whale oil isn't as common now) they are then placed in a silicone sock and stored in a safe with a golden rod, inside the basement where the temperature does not fluctuate much. Never had an issue. Of course this is before the boating accident.

Depends on exposure to salt and humidity. If you store them in a climate controlled environment there isn't a need to clean unused ones much if at all. Throw some firearm desiccant packs inside the cases or safe if you're concerned.