Corrosion, from corrosive ammo, is a "funny" thing.
I have an M&P 15 in 5.45X39. At first, I cleaned it the day I shot it. Then something came up and I didn't get to it one day and I noticed a couple days later, when I cleaned it, there was no sign of corrosion. So I decided to experiment. I was out to 2 weeks after shooting it before I cleaned it. No issues. I was beginning to convince myself that the Russian surplus I was shooting really wasn't corrosive after all.
Then, I shot it on a Saturday, came home from NC left it sit overnight. I only looked at it Sunday morning because it was a pretty day, I had nothing else to do and I figured I'd sit out on the deck in the sun and clean my rifle. HOLY COW!!! I had to pound the bolt back, the lugs on the bolt and the locking recesses in the barrel extension were covered in rust. The tail on the bolt looked like it had orange fungus growing on it and had already pitted - in less than 24 hrs., and I run my ARs so wet the oil slings back on my face/hands when I shoot them. The flash suppressor was rusting as well.
I took it to the kitchen sink (wife was at church, so no questions) and used the sprayer to spray hot water down the barrel, down the gas tube, all in the upper receiver, in the lower receiver, I laid the bolt/carrier down in the water and let them sit and then swirled them around some. Then I took everything outside, dried it off with a hair dryer (again, the wife was at church, so I used her hair dryer) and dried it off, scrubbed off the rust, cleaned it up, lubed it and put it away. Then I checked it again every day for the next three to make sure I didn't miss something.
I was sick. I mean sick. I've never seen so much rust/corrosion on anything I own (I've never let my guns rust - I over lube/wipe down everything, oil on me washes off, lack of lube on the gun leads to rust/malfunctions).
The point is, don't get complacent. The salts draw moisture from the air and concentrate it where ever the salt deposits are in the weapon. You might get by a little longer in a relatively dry climate but get some humidity and the salts do their worst to corrode your weapon.
