Anyone care to weigh in on how synthetic and standard motor oils as well as ATFs do for long term storage. How good of a rust inhibitor are they?
I don't know about ATF, but I'm sure some dedicated gun oils are better corrosion protectants than Mobil 1 is, because corrosion protection rather than lubrication is the higher priority for many gun products. On the exterior of a gun, Mobil 1 is too messy to be practical anyway due to the thick film it forms.
For long term storage, a corrosion protectant like Corrosion-X or Boeshield T-9 is probably a better product than any oil, gun-marketed or not. I've never had any internal rust with Mobil 1, but if I were going overseas for a year and leaving my guns in storage, I'd clean the lube off and use a corrosion protectant. I have an antique Mosin-Nagant M39, and I use Boeshield on the part of the barrel and action inside the stock, since I almost never take the stock off.
Boeshield is a pretty remarkable product, if a little messy until it dries. I have a set of tow chains that have been sitting in a steel ammo can in the garage between uses since 1995, in humid Florida and eastern NC, and they still look brand new.
Honestly, I have to think the lubricating qualities of a gun oil matter less that the corrosion protective ones in most cases. I can't ever remember having a functional failure caused by poor lubrication, but I can remember instances where a surface I thought was protected ended up with a coating of rust.
For non-semiautos, especially those that go a long time between range trips, corrosion protection is definitely the top priority.
For semiautos, though, the lubrication properties are at least as important; I once had some galling on the bolt of a stainless Mini-14 lubricated with a gun oil that was more corrosion protectant than lubricant, and my wife had a Russian SKS lubricated with Rem Oil that stopped cycling properly when the lube dried out over time and the carbon solidified. So I think the lubrication properties do matter for semiautos.
did you go check out the thread he linked and its results??? Hint: The synthetic motor oil didn't do nearly as well as some of the gun products
That test primarily measured corrosion protection and shear strength, not lubrication ability. Yes, synthetic oils are not as good as corrosion protectants as are products designed as corrosion protectants, and yes, they have higher shear strength than thinner oils. They are better lubricants, though, and shear strength is actually a plus rather than a minus for lubricating bearing surfaces (otherwise thinner lubricants would always lubricate better).
Gun bearing surfaces in a semiauto are small and more highly loaded than a couple of mild steel plates with dozens of square inches of contact area and no load. Put fifty or a hundred pounds per square inch on the top plate and then see which oil makes it slide better. Oil shear on the bearing surfaces of an AR is a negligible drag on the action, but metal-to-metal friction is not, particularly if solid powder fouling is allowed to accrete due to the surfaces drying out.