For hunting? Never used one myself. Just keep a thin film of oil on all the exposed metel, and a good cleanup when I get home and no problems that way. To me they are just a waste of money when you can protect your weapon from the elements with a .2 cent dollop of oil and a good cleanup afterwards.
Now if you are talking about for storage where you dont have humidity control or something, Ive found that those "gun socks" sold at most sporting goods retailers are great. They are silicone impregnated and will keep the moisture off your weapon. Most of My M1 collection wears them except for the big dogs that I have in the humidity controled gun safe!!
We all spend our time at the range, making sure our rifle is shooting just right. We get it dialed in, and then we head to the woods, ready to shoot our animal. Well, what happens if the animal comes out where you do not expect it? Will you be able to make the shot?
This scenario has happened to me. My first deer I ever shot, I had to shoot left handed. I had never practiced that way, and paid for it by having my nose broken with the scope. If I had just...