Whatever the case, use something. Especially in a semiautomatic like an AR rifle.
Do not use WD-40. It may be better than nothing, but it is not designed to be a lubricant. It is a water displacing rust preventative with a peculiar cult following.
A friend says he uses and likes "ALG Go juice", but plans to switch to "Duck Sauce". ALG Go Juice is available on Amazon for $15 per 4 ounce bottle.
Olive Oil is not recommended. It tends to degrade over time in a way that yields a gummy substance.
Canola Oil is a better choice, if you are considering plant sourced lubricants. I have read that it was first developed as a candidate for an engine lubricant. But you can easily do better.
It has been suggested: "If you hang around gunshops, shooting matches or such events, you'll have a lifetime supply of perfectly fine gun lubricants samples.
Many people use automotive oil. One person says that he saves the drippings (of fresh oil) when he does oil changes and thus obtains a mix that more than supplies his needs for lubing all his guns. At one time "Mobil 1 synthetic" was recommended, and it still is. It isn't clear that it is any better than any other synthetic that is readily available at your local auto parts store.
Strangely, oils labeled "full synthetic" are now legally allowed to be a blend of synthetic and other oils. This being true, the idea of just using any old motor oil gains weight.
Amsoil does sell things labeled 100 percent synthetic. A product from them labeled "Amsoil 100 percent synthetic V-Twin motorcycle oil 20-50" is endorsed by several and is available on Amazon for $29 per quart. I think this would be an excellent choice. Notice that 100 percent synthetic has different meaning than "full synthetic". I am not sure what "full synthetic" means in this day and age, but you are on safe ground with 100 percent synthetic.
I got up one Saturday morning, went to the parts desk at my Toyota dealership and bought a quart of 0-20 Toyota synthetic motor oil The price was $8.08 for the quart. This is certainly better than the $12.00 per quart for Mobil 1 at the local auto parts store. And people say it is better too, being 100 percent synthetic. Some Toyota owners will use nothing else for that very reason (in their vehicles) I will find it entertaining to use the same oil on my guns that I do in my vehicle.
Perhaps the used oil from my vehicle would work just fine as a gun lubricant. I change my sythetic oil at 5000 miles and Toyota claims I could go to 10,000 miles. At 5000 miles it should have a lot of life left in it. But with a quart of fresh oil on hand, I probably have a lifetime supply.
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