Not all synthetic oils are equal.
AMSoil is good stuff, however if I were going to use a motor oil on my guns I'd probly use Motul.
AMSoil is a PAO based oil with Esters added to it.
Motul's 8100 and 300v line's are Ester based with additional Esters added.
Ester based oils 'soak' into the metal and stay there. There's a somewhat famous test done by BMW where they dipped crankshafts into an oil bath and then left them outside in the elements for 6 months. Only Motul showed no rust. I dont believe AMSoil was in the test, so you cant compare them, but regardless Ester based oils are the best available right now.
The 4-ball wear test is probly the most similar to replicating what happens when you fire a gun.
Something to keep in mind for those that like to use motor oil to lube their guns.
FWIW, I liked Militec as a lube, but not as a corrosion preventer. I've been using Weapon Sheild and so far it's the best I've used. Militec with Break-Free worked well as a combo, but it's just easier and cheaper to use one product.