One of the issues as mentioned is when it "runs dry". The new stuff such as G96 is also a metal conditioner. When it's dry. It's not actually dry since the oil is in the pores of the metal. As a result it's still protected if it's seasoned in the stuff. Shoot then just wipe the carbon off.
As for motor oils. I considered using the 0W-40 Shell Roteilla full synthetic that my F350 7.3 liter powerstroke uses. Improved fuel economy immediately and cold starts (-50 no problem with engine block heater and oil pan heater). But it's not worth it. The good stuff doesn't cost much more for how much you use. So I never went through with it.
We use Mobil 1 5-40 in all our equipment. There is no question the superiority of synthetic oils. On the OM444LA, we noticed with conventional oil that there was a buildup of sludge in the intercooler pipes. Basically a thin sticky layer on all surfaces of the inside of the pipe. When we changed over to Mobil 1, I later had the intercooler pipes off again, they were clean inside and there was no sludge, but only small pools of oil in the low spots.
I would use mobil 1 on my firearms if it wasn't for trusting grease on mine so much. Using a premium quality moly grease on a NP22, all areas including the barrel, we ran a non-stop string of 200+ rounds though it. The barrel and grease were smoking and had dried up a bit, but was still adiquately lubricating the barrel. That night, it wiped away clean with a paper towel, there was no scrubbing or hard work. Wipe dirty grease away, replace with fresh clean grease. I've currently got 1000 rounds on the grease job on my P226, I think in another 500 I will clean and regrease. I've only got 250 rounds so far on my 1911.
All parts scrubbed clean in a varsol cleaning tank, rinsed clean with water then blown dry with compressed air. The parts have a grey tinge to them and look very dry.
All parts greased and assembled. All areas of the pistol have been covered in grease. This picture is prior to wiping down with a rag and hand cycling of the action to clear out the excess grease.
After numerous wipe downs, using a oil dampened spot on a rag, I try to leave a thin exterior coating of grease, the little bit of oil helps to strip the last little bit from the surface but not the pores of the finish. After final cleaning the finish holds a nicer dark color longer than oil alone does.
I don't have any pictures of it, but I do find that debris does collect on the grease but that doesn't bother me for the following reason. If the debris is small enough to fit between any sliding part, it will be completely encapsulated in grease and will not contact the surface. It will not stay in one location, but will eventually be expelled due to it moving slower in the grease. If it is too large to fit between any sliding part, it will get stuck to the grease and be pushed out of the way of the sliding part. When the surface of the grease becomes saturated with debris, it no longer sticks so the dirty grease acts as a protective seal.
Eventually the grease will break down as well as work its way out of the contact areas, but like anything that needs to be greased, it will always need more grease applied over time.
When you apply grease, it stays where you applied it, not running down the stock of your rifle to the bottom your safe. Grease has a much longer usable lifespan than oil and as such gives you a much better indicator of when its time to regrease. Grease is generally easier to clean and re-lubricate than oil, oil is more likely to need a greater amount of elbow grease.
One disadvantage, is that any time you are dealing with greasing and getting the firearm clean before it is range ready, you're going to get covered in grease. Once properly cleaned away, you don't get covered in it... as much.
I would take oil over any cheap grease any day though. Only premium quality grease is worth using.