A US Marine Corps sergeant writes about using synthetic motor oil as a very effective and efficient weapon lubricant in extreme climates.
Problems would occur when troops were engaged for prolonged times and couldn’t risk breaking down their weapons to clean out all the dirt. We would simply pour in more CLP. An AR-15 type rifle will fire and function dirty as long as it is liberally lubricated. The problem is the more oil you pore down the bolt and into the chamber the more dirt it collects. What we discovered is that using Mobil1 synthetic motor oil usually in a 0w30 or 5w30 works much better than the CLP. At $10 per quart it is on the expensive side as motor oils go. But when compared to CLP or Rem Oil that are usually sold in 6 ounce containers at $5 to $6 it is much more cost effective. We also experimented with it on out crew served weapon systems. We found it to out perform the Lubricant, Small Arms (LSA) used on the M2 (.50 Cal Browning machinegun) and MK-19 (40mm grenade launcher).
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I still recommend cleaning your weapon as frequently as possible. In the Corps we would hold random weapons inspections and any NCO could demand to see the bolt on any junior Marine’s weapon at anytime. I also want to mention that we never tested traditional (non-synthetic) motor oil on our weapons but the use of motor oil for cleaning and lubrication of weapons systems has been recognized by the US Military as early as WWII and can be found in numerous field manuals.
There's more at the link.
My military experience was decades ago, in a war on a different continent; but the lessons we learned in African dust and dirt were very similar. We used gasoline or diesel fuel as a quick-and-dirty field cleaning fluid, and then used motor oil as a lubricant. If you didn't dry off all the gasoline, or mixed it with motor oil, this could lead to flaming embarrassment when firing a test round or two, but apart from that, the combination worked just fine. Later, I learned that automatic transmission fluid (ATF) was even better than gasoline for cleaning and lubrication.
Today, I keep a bottle of ATF and a five-quart jug of synthetic motor oil in my garage (I use this brand because I drive an older car), to have a long-term reserve of gun cleaning and lubrication fluids.
There's also a very good bore cleaner and general firearm cleaning fluid known as "Ed's Red". You can easily mix it yourself. There are recipes for it all over the Internet; here's one that is typical of the others. You can follow it with synthetic motor oil for lubrication.