Pick up a copy of the Brownells or Midway USA catalogs, and you can find a wide selection of gun oils and protectants that are supposed to provide corrosion protection for your firearms. But how can you tell which ones are the best?
Fortunately, several people have done some research to help give you an idea on which oils provide good rust resistance.
Over at 6mmBR.com, there is an article called “Corrosion Protection Products: How to Keep Your Rifle Rust-Free in Storage.” In this evaluation, corrosion protectants were tested: Break-Free, Corrosion-X, Eezox, FP10, Rem-Oil, Slip2000, Strike-Hold, and Mobil 1 15W50 (motor oil). Using a salt water spray in the testing, they found Eezox and Corrosion-X provided the best protection, though I was very impressed by Break-Free’s performance.
I also encourage you to check out the article “GUN CLEANING CLINIC: Knowing The Limits Of Rust Preventives” on the Brownells website. In this test, the following products were tested:  Birchwood Casey Sheath, Boeshield T-9, Break-Free CLP, Break-Free Weapon Wipes, Brownells Cosmoline, Brownells Rust Preventive No. 2, Hoppe’s Lubricating Oil, Rig Universal Grease, Tetra Gun Lubricant, Valvoline 5W-30 motor oil, and WD-40. In the Brownells test, the samples were left in an outdoor environment for 72-hours, during which they experienced high temperatures and a rainstorm.
The best performers in the Brownells test were Boeshield T-9, Brownells Cosmoline, and Rig Universal Grease for long term storage, and Brownells RP2, Tetra Gun, and WD-40 for corrosion resistance that is usable on your daily carry guns.
Of course, both tests tend to demonstrate the extremes of hardship on your guns. I would imagine with just a little care, any of the products would be capable of protecting your firearms. However, everyone can, on occasion, get caught in a rainstorm or otherwise expose their gun to the elements. In those cases, picking one of the better protectants may prevent some rust from showing up on your hunting rifle or concealed carry pistol.
